The  D.  Van  Nostrand  Company 

intend  this  book  to  be  sold  to  the  Public 
at  the  advertised  price,  and  supply  it  to 
the  Trade  on  terms  which  will  not  allow 
of  discount. 


TOLL   TELEPHONE 
PRACTICE 


BY 
J.  BERNHARD  THIESS,  B.S.,  LL.B. 


»  I 
AND 


GUY  A.  JOY,  B.E. 

WITH  AX  INTRODUCTORY  CHAPTER  BY 
FRANK    F.    FOWLE,    S.B. 


273  ILLUSTRATIONS 


NEW  YORK 
D.    VAN    NOSTRAND    COMPANY 

TWENTY-FIVE  PARK  PLACE 
1912 


COPYRIGHT,  1912,  BY 
D.  VAN  NOSTRAND    COMPANY 


Stanbope  flttcss 

F.  H.GILSON  COMPANY 
BOSTON,  U.S.A. 


PREFACE 

THE  art  of  telephony  has  now  progressed  so  far  in  its  development 
that  great  difficulty  accompanies  any  attempt  to  present  it  as  a  whole 
in  exhaustive  form,  in  any  treatise  of  reasonable  length.  This  state- 
ment, in  the  belief  of  the  authors,  will  be  almost  universally  accepted 
by  all  who  are  broadly  familiar  with  the  subject,  and  thus  seems 
to  justify  the  present  volume  which  deals  alone  with  toll  practice. 
While  the  field  of  interest  naturally  diminishes  as  the  scope  of  the 
subject  becomes  limited,  it  is  still  the  hope  of  the  authors  that  in 
departing  from  previous  general  customs  and  attempting  a  compre- 
hensive treatment  of  only  a  portion  of  the  art,  their  labors  will  receive 
some  appreciation. 

The  theoretical  portions  of  the  subject  have  been  treated  as  far 
as  possible  from  a  non-mathematical  point  of  view,  with  the  object 
of  appealing  not  only  to  the  engineer  and  the  student,  but  as  well 
to  those  whose  training  has  been  essentially  practical.  For  the  same 
reason  purely  theoretical  considerations  have  been  treated,  where 
possible,  in  connection  with  their  practical  applications,  with  the 
further  object  of  holding  the  reader's  interest. 

The  authors  wish  to  acknowledge  the  contribution  of  the  introduc- 
tory chapter  by  Mr.  Frank  F.  Fowle,  and  also  many  helpful  sugges- 
tions in  the  preparation  of  the  manuscript.  They  also  wish  to 
acknowledge  their  indebtedness  to  Mr.  J.  E.  Hilbish,  who  collaborated 
in  numerous  original  articles  which  have  been  used  in  whole  or  in 
part.  Many  authorities  have  been  consulted  on  all  phases  of  the 
subject,  to  whom  the  authors  tender  their  thanks. 

J.  B.  T. 

G.  A.  J. 

CHICAGO,  ILL.,  MAY,  1912. 


268950 


TABLE   OF    CONTENTS 


CHAPTER  PAGE 

I.  INTRODUCTION i 

II.  RURAL  TELEPHONE  EQUIPMENT n 

III.  TOLL  CUT-IN  STATIONS 29 

IV.  TOLL  POSITIONS  AT  A  LOCAL  SWITCHBOARD 41 

V.  TOLL  SWITCHING  SYSTEMS 55 

VI.  SMALL  TOLL  SWITCHBOARDS 59 

VII.  MULTIPLE-DROP  TOLL  SWITCHBOARDS 75 

VIII.  MULTIPLE-LAMP  TOLL  SWITCHBOARDS 112 

IX.  TOLL  CONNECTIONS  TO  LOCAL  AUTOMATIC  SYSTEMS 156 

X.  SUPERVISORY  EQUIPMENT  AND  TOLL  CHIEF  OPERATOR'S  DESK 165 

XI.  TOLL  WIRE  CHIEF'S  DESK 174 

XII.   SIMPLEX  SYSTEMS 187 

XIII.  COMPOSITE  SYSTEMS 195 

XIV.  PHANTOM  LINES 211 

XV.  TEST  AND  MORSE  BOARDS : 216 

XVI.  SMALL  TEST  PANELS 237 

XVII.  LINE  CONSTRUCTION 245 

XVIII.  ELECTRICAL  REACTIONS  IN  TELEPHONE  LINES i . .  307 

XIX.   CROSS  TALK  AND  INDUCTIVE  DISTURBANCES 334 

XX.   METHODS  OF  TESTING 37° 

XXI.  TOLL  LINE  MAINTENANCE 394 

XXII.  THE  TELEPHONE  REPEATER 399 


vii 


LIST  OF  TABLES 


TABLE  PAGE 

1.  PROPERTIES  OF  HARD-DRAWN  COPPER  WIRE 251 

2.  BROWN  AND  SHARPE  WIRE  GAUGE 252 

3.  TEMPERATURE  EFFECTS  IN  SPANS  OF  HARD-DRAWN  COPPER  WIRE 256 

4.  TABLE  OF  SAG  IN  HARD-DRAWN  COPPER  WIRES,  FROM  THE  PRACTICE  OF  THE 

AMERICAN  TELEPHONE  AND  TELEGRAPH  COMPANY 260 

5.  AVERAGE  LIFE  OF  POLES 261 

6.  APPROXIMATE  SIZES  OF  POLES 262 

7.  TENSILE  STRENGTH  OF  POLE  WOODS  IN  POUNDS  PER  SQUARE  INCH 269 

8.  DIMENSIONS  OF  STANDARD  CROSS-ARMS 277 

9.  DEPTH  OF  POLE  SETTING 280 

10.  DIMENSIONS  OF  ANCHOR  LOGS 289 

11.  STRENGTH  OF  WROUGHT-IRON  ANCHOR  RODS 290 

12.  SIZE  AND  HOLDING  POWER  OF  MATTHEWS  GUY  ANCHORS 292 

13.  ELECTRICAL  PROPERTIES  OF  TRUNK  AND  TOLL  CABLES , 314 

14.  CROSS-TALK  EXPOSURES  IN  TERMS  OF  STANDARD  TRANSPOSITION  SECTIONS...  346 

15.  RESISTANCE  PER  MILE  OF  IRON  AND  COPPER  LINE  WIRE  AT  68°  F 376 

16.  BRIDGE  ARM  RATIOS 380 


CONDENSED   LIST   OF   ILLUSTRATIONS 


Toll  Board  of  the  American  Telephone  &  Telegraph  Company  at  Philadelphia,  Pa. 

Frontispiece 
FIGURE  PAGE 

1.  Standard  Plug  and  Jack  Designations . . .  . 14 

2.  Grounding-Button  Telephone,  Using  One  Side  of  Metallic  Line 17 

3.  Grounding-Button  Telephone,  Using  Both  Sides  of  Metallic  Line 18 

4.  Pulsating  and  Alternating  Current  Telephone  for  Use  on  Grounded  Line ....  20 

5.  American  Electric  Telephone  Company's  Switchboard  Circuit  for  Pulsating 

and  Alternating  Telephone 21 

6.  Four-Party  Selective  System  for  Grounded  Lines 24 

7.  Eight-Party  Selective  System  for  Metallic  Lines 26 

8.  Double  Supervision  Cord  Circuit . .  27 

9.  Double  Supervision  Cord  Circuit  Using  Repeating  Coil 28 

10.  Bridging  Party  Line 31 

11.  "Waterloo"  Station  Equipment 33 

12.  Toll  Cut-in  Station  with  Key  Equipment 33 

13.  Approved  Method  of  Wiring  Key  Equipment  at  Toll  Cut-in  Station 34 

14.  Toll  Cut-in  Station  for  Grounded  Lines 34 

15.  Telephone  Station  Switch  for  Use  with  Two  Grounded  Lines 35 

16.  Toll  Station  Switch  for  Connecting  Grounded  and  Metallic  Lines 35 

17.  Repeating-Coil  Connection  between  Metallic  and  Grounded  Lines 37 

18.  Key-Type  Equipment  at  a  Toll  Cut-in  Station 39 

19.  Jack-Type  Equipment  at  a  Toll  Cut-in  Station 40 

20.  Wiring  of  a  Toll  Terminal  for  a  Small  Switchboard 41 

21.  Toll-to-Toll  Connection  at  a  Small  Magneto  Switchboard 42 

22.  Toll-to-Toll  Connection  with  Repeating  Coil 43 

23.  Toll-to-Toll  Connection  Using  a  Transfer  Circuit 45 

24.  Toll-to-Local  Connection  in  a  Magneto  Multiple  Switchboard 47 

25.  Toll-to-Local  Connection  in  a  Common-Battery  Non-Multiple  Switchboard. .  49 

26.  Toll-to-Local  Connection  in  a  Common-Battery  Multiple  Switchboard 51 

27.  Section  of  Common-Battery  Multiple  Switchboard  Showing  Toll  Position.  ...  53 

28.  T}rpical  Lay-out  of  a  Toll  System 58 

29.  Method  of  Transferring  Toll  Lines  for  Night  Service  by  Means  of  Dummy 

Plugs 60 

30.  Method  of  Transferring  Toll  Lines  for  Night  Service  by  Means  of  Keys 60 

31.  Method  of  Transferring  Toll  Drops  for  Night  Service  by  Means  of  Keys 61 

32.  Jack  and  Key  Equipment  of  a  Single-Position  Toll  Board 62 

33.  Jack  and  Key  Equipment  of  a  Two-Position  Toll  Board 64 

34.  Two- Way  Toll  Trunk  between  a  Non-Multiple  Toll  Board  and  a  Common- 

Battery  Multiple  Local  Board 67 

35.  Diagram  of  a  Complete  Toll  Connection 7° 

36.  Type  of  Incoming  Toll  Trunk  Used  with  a  Non-Multiple  Toll  Board 72 

37.  Type  of  Recording  Toll  Trunk  Used  with  a  Non-Multiple  Toll  Board 73 

38.  Two- Way  Toll  Trunk  with  Busy-Test  Key 74 

39.  Toll-to-Toll  Connection  at  a  Multiple-Drop  Toll  Board 79 

40.  Toll-to-Local  Connection  at  a  Multiple-Drop  Toll  Board 81 

41.  Combination  Cord  Circuit  for  a  Multiple-Drop  Toll  Board 82 

42.  Recording  Connections  for  a  Multiple-Drop  Toll  Board  at  St.  Louis,  Using  a 

Three-Wire  Trunk 84 

43.  Toll-to-Local  Connection  Using  Two- Wire  Trunk  at  St.  Louis 87 

44.  Two- Wire  Recording  Trunk  Circuit,  Kinloch  Company,  St.  Louis 90 

xi 


xii  CONDENSED   LIST  OF  ILLUSTRATIONS 

FIGURE  PAGE 

45.  Toll  Connection,  Using  a  Three-Wire  Combined  Switching  and  Recording 

Trunk,  of  the  American  Telephone  &  Telegraph  Company's  Type 93 

46.  Stromberg-Carlson  Multiple  Drop  Toll  Switchboard,  Installed  at  Toledo, 

Ohio 97 

47.  Toll   Connection,  Using   a   Two-Wire  Combined  Switching  and   Recording 

Trunk,  of  the  American  Telephone  &  Telegraph  Company's  Type 99 

48.  Interposition  Trunk  Circuit 103 

49.  Shifting  Receiving  Circuit  at  Recording  Positions 105 

50.  Jack  and  Key  Equipment  of  a  Toll  Line  Terminal  Section  in  a  Multiple-Drop 

Switchboard 108 

51.  Jack  and  Key  Equipment  of  a  Combined  Recording  and   Common-Drop 

Section 109 

52.  Multiple-Lamp  Toll  Switchboard;   American  Telephone  &  Telegraph  Com- 

pany, at  Lynchburg,  Va in 

53.  General  Type  of  Toll-to-Toll  Connection  for  a  Multiple-Lamp  Toll  Board. ...  113 

54.  Toll-to-Local  Connection  through  a  Multiple-Lamp  Board  of  the  American 

Telephone  &  Telegraph  Company's  Type 118 

55.  Recording  Trunk  Circuit  Used  by  the  American  Telephone  &  Telegraph  Com- 

pany   122 

56.  Incoming  Toll  Trunk  of  the  American  Telephone  &  Telegraph  Company's 

Type,  Showing  Four-Party  Through  Ringing 127 

57.  Tri-State  Telephone  &  Telegraph  Company's  Multiple-Lamp  Toll  Board,  in 

Use  at  St.  Paul,  Minnesota 131 

58.  Toll-to-Local  Connection,  as  Used  by  the  Tri-State  Telephone  &  Telegraph 

Company , 133 

59.  Toll  Recording  Connection,  Used  by  the  Tri-State  Telephone  &  Telegraph 

Company 135 

60.  Toll  Recording  Connection,  Used  by  the  Tri-State  Telephone  &  Telegraph 

Company 136 

61.  Toll-to-Local  Connection  of  the  United  States  Telephone  Company's  Type, 

Used  at  Cleveland,  Ohio 141 

62.  Toll  Recording  Circuit,  Used  by  the  United  States  Telephone  Company  at 

Cleveland,  Ohio 144 

63.  Interposition  Trunk  Circuit,  Used  by  the  United  States  Telephone  Company 

in  their  Exchange  at  Cleveland,  Ohio 146 

64.  Multiple  Toll  Board  of  the  American  Telephone  &  Telegraph  Company  at 

Philadelphia,  Pa.,  Showing  Pneumatic  Ticket-Distributing  System 149 

65.  Detail  of  Wiring  of  a  Toll  Line  Terminal  in  a  Multiple-Lamp  Toll  Board ....  150 

66.  High  Potential  and  Abnormal  Current  Arresters 151 

67.  View  of  Toll  Operating  Room,  at  Grand  Rapids,  Michigan 157 

68.  View  of  Toll  Operating  Room,  at  Dayton,  Ohio 159 

69.  Diagram  of  a  Toll-to-Automatic  Connection,  at  Dayton,  Ohio 160 

70.  Diagram  of  a  Recording  Toll  Trunk,  at  Dayton,  Ohio 162 

71.  Diagram  of  a  Toll  Board  Trunk  from  a  Line  Position  to  a  Rural  Position,  at 

Dayton,  Ohio 162 

72.  Diagram  of  the  Automatic  Electric  Company's  Toll-to-Automatic  Connection.  163 

73.  Diagram  of  a  Toll  Supervisor's  Trunk  Circuit 167 

74.  Diagram  of  Chief  Operator's  Listening  and  Monitoring  Taps 169 

75.  Chief  Operator's  Instruction  Circuit 171 

76.  Chief  Operator's  Pilot  Taps 172 

77.  Chief  Operator's  Tell-tale  Circuit 172 

78.  Wiring  of  Toll  Line  Circuit  at  Wire  Chief's  Desk 176 

79.  Face  Equipment  of  a  Wire  Chief's  Desk 177 

80.  Arrangement  of  Jacks  at  Wire  Chief's  Desk 178 

81.  Wire  Chief's  Testing  Circuit 178 

82.  Circuit  for  Preliminary  Tests 181 

83.  Wire  Chief's  Testing  Trunk 182 

84.  Wire  Chief's  Cord  Circuit 184 

85.  Two-position  Toll  Wire  Chief's  Desk 185 

86.  Theoretical  Diagram  of  a  Simplex  Circuit 188 

87.  Simplex  Circuit,  Using  a  Repeating  Coil 189 

88.  Simplex  Circuit,  Using  Retardation  Coils 190 

89.  Diagram  of  an  Intermediate  Telegraph  Station  on  a  Simplex  Line 191 


CONDENSED   LIST   OF   ILLUSTRATIONS  Xlil 

FIGURE  PAGE 

90.  Diagram  of  a  Terminal  Telegraph  Station  on  a  Simplex  Line 192 

91.  Terminal  Telephone  Station  and  Telegraph  Repeater 193 

92.  Grounded  Line  Composited  for  Telegraph  Service 196 

93.  Retardation  Coil  Suitable  for  Composite  Work 197 

94.  Wave  Form  of  Telegraph  Current  in  Composite  Circuit 198 

95.  Metallic  Line  Composited  for  Telegraph  Service 199 

96.  Method  of  Ringing  on  Composite  Line 201 

97.  Low  Frequency  Alternating  Current  Relay 202 

98.  High  Frequency  Alternating  Current  Relay 203 

99.  Railway  Composite  Circuit 207 

100.  Retardation  Coil  Type  of  Phantom  Circuit 211 

101.  Repeating  Coil  Type  of  Grounded  Phantom  Circuit 212 

102.  Repeating  Coil  Suitable  for  Phantom  Use 213 

103.  Repeating  Coil  Type  of  Phantom  Circuit 213 

104.  Phantom  Circuit  Used  as  an  Order  Wire 214 

105.  Toll  Line  Circuit  at  Test  Board 217 

106.  Composite  Cord  Circuit  at  the  Test  Board 218 

107.  Simplex  Cord  Circuit  at  the  Test  Board 218 

108.  Battery  Jacks  at  the  Test  Board 219 

109.  Telegraph  Monitoring  and  Test  Circuit 219 

no.   Wire  Chief's  Telephone  Circuit  at  Test  Board 220 

in.   Voltmeter  or  Ammeter  Circuit  at  Morse  Board 221 

112.  Bridge  Circuit  at  Test  Board.  . 221 

113.  Galvanometer  Circuit  at  Test  Board 222 

114.  Jack  and  Key  Equipment  of  a  Standard  Test  and  Morse  Board 223 

115.  Legless  Telegraph  Key 224 

1 16.  Leg-Type  Telegraph  Key 224 

117.  Telegraph  Sounder 225 

118.  Telegraph  Relay 225 

119.  Composite  Connection  at  Cordless  Test  and  Morse  Board 227 

1 20.  Simplex  and  Phantom  Connection  at  a  Cordless  Test  Board 231 

121.  Face  Equipment  of  a  Cordless  Test  and  Morse  Board 233 

122.  Leased  Line  Circuit ^ 234 

123.  Construction  cf  Jack  Panels  for  Test  and' Morse  Boards 235 

124.  Forty-Wire  Test  Panel 238 

125.  Twenty-Wire  Test  Panel 239 

126.  Western  Electric  Company's  Twenty-one-\Vire  Toll  Test  Panel 240 

127.  Wiring  of  Line  Circuit  for  Small  Test  Panel 241 

128.  Jack  Arrangement  in  Small  Test  Panel 241 

129.  Line  Wiring  of  Small  Test  Panel,  Arranged  for  Crcss-Connection 242 

130.  General  Arrangement  of  Apparatus  for  a  Small  Test  Panel 243 

131.  Western  Electric  Company's  Forty-one-Wire  Toll  Test  Panel  Extension 244 

132.  Simplex  Wiring  for  Small  Toll  Test  Panel 244 

134.  Illustration  of  Ice-coated  Wire ' 257 

135.  Effect  of  Ice  Formation  on  Line  Wire : 258 

136.  Cross  Section  of  Concrete  Pole 263 

137.  Treated  Pine  Pole 266 

138.  Untreated  Chestnut  Pole 266 

139.  Effect  of  Sleet  on  Pole  Line 268 

140.  Diagram  of  Forces  Acting  on  a  Corner  Pole 269 

141.  Effect  of  Sleet  on  a  Poorly  Constructed  Pole  Line 272 

142.  Effect  of  Sleet  on  a  Properly  Braced  Pole  Line 273 

143.  Ungraded  Pole  Line 274 

144.  Graded  Pole  Line 274 

145.  Pole  with  Gains  Cut  for  Cross-Arms 276 

146.  Standard  Ten-Pin  Cross-Arm 277 

147.  Standard  Cross-Arm  Brace 278 

148.  Standard  Method  of  Bracing '  278 

149.  Standard  Sizes  of  Pins 279 

150.  Pike  Pole 281 

151.  Dead  Man 281 

152.  Pole  Support 281 

153.  Raising  Fork 281 


XIV  CONDENSED  LIST  OF  ILLUSTRATIONS 

FIGURE  PAGE 

154.  Cant  Hook 282 

155.  Facing  of  Cross-Arms  on  Pole  Line 282 

156.  Tamping  Bar 284 

157.  Method  of  Setting  Poles  in  Marshy  Ground 283 

158.  Method  of  Bracing  Pole  in  Marshy  Soil 285 

159.  Side  Guying 285 

160.  Head  Guying 286 

161.  Double  Head  Guying 286 

162.  Head  Guying  on  Grades 286 

163.  Guy-Stub  and  Anchor .  .  . 287 

164.  Method  of  Bracing  Guy-Stub 288 

165.  Standard  Guy-Rod 289 

166.  Miller  Anchor 290 

167.  Matthew's  Anchor 291 

168.  Theory  of  Holding  Power  of  Matthew's  Guy  Anchor 292 

169.  Guying  to  Tree  Trunks 294 

1 70.  Guying  to  Tree  Limbs 294 

171.  Rock  Guying 295 

172.  Miller  Rock  Anchor 296 

1 73.  Guying  at  Curves  and  Corners 297 

1 74.  Double  Pole  Braces 298 

175.  Three-Bolt  Guy  Clamp 299 

176.  Standard  Thimble 299 

177.  Standard  Line  Insulator  and  Two-Piece  Transposition  Insulator 300 

178.  Double-Petticoat  Line  Insulator  and  One-Piece  Transposition  Insulator.  ....  301 

1 79.  Pay-out  Reel 301 

180.  Wagon  Pay-out  Reel 301 

181.  Running  Board 302 

182.  Come-Along 303 

183.  Pulling  up  Line  Wire 303 

184.  Method  of  Tying  Wire  to  Insulator 304 

185.  Location  of  Wire  on  Insulators 305 

186.  Dead  Ending 305 

187.  Cook  Wire  Joint 306 

188.  Cross  Section  of  Armored  Cable 313 

189.  Artificial  Line  with  Distributed  Capacity 314 

190.  Outgoing  and  Incoming  Currents  on  a  Cable  with  a  Constant  Impressed 

E.M.F 315 

191.  Effect  of  Closing  Key  Momentarily 316 

192.  Effect  of  a  Succession  of  Impulses 316 

193.  Cable  Telephone  Circuit 316 

194.  Mechanical  Analogy  of  a  Loaded  Circuit 319 

195.  Method  of  Inserting  Pupin  Coils  in  Telephone  Line 323 

196.  Sinusoidal  Wave 323 

197.  Complex  Voice  Wave 324 

198.  Current  Values  in  Heavily  Loaded  Cable 328 

199.  Current  Values  in  Cable  with  Medium  Loading 329 

200.  Current  Values  in  Loaded  No.  8  B.W.G.  Copper  Open  Wire  Circuit 330 

201.  Current  Values  in  Loaded  No.  12  B.S.G.  Copper  Open  Wire  Circuit 331 

202.  Character  of  Magnetic  Field  Surrounding  a  Single  Isolated  Conductor 336 

203.  Lines  of  Force  between  Oppositely  Charged  Plates 337 

204.  Induced  Electric  Charges 338 

205.  Electrostatic  Induction  between  Parallel  Wires 338 

206.  Carty's  Experimental  Circuit 339 

207.  Carty's  Experimental  Circuit _ 340 

208.  Arrangement  of  Disturbing  Wire  and  Metallic  Circuit  for  Prevention  of  In- 

duction    341 

209.  Unbalanced  Exposures  and  Resulting  Induction 341 

210.  Effect  of  Single  Transposition  on  Electromagnetic  Induction 342 

211.  Effect  of  Single  Transposition  on  Electrostatic  Induction 342 

212.  Example  of  Improper  Transpositions 343 

213.  Example  of  Correct  System  of  Transpositions 344 

214.  Derivations  of  Standard  Transposition  Types 345 


CONDENSED  LIST   OF  ILLUSTRATIONS  XV 

FIGURE  PAGE 

215.  Transposition  Scheme  for  a  Ten-Wire  Line 347 

216.  Standard  Transposition  Scheme  for  Twelve- Wire  Line 349 

217.  Standard  Transposition  Scheme  for  Forty- Wire  Line 349 

218.  A-B-C  Transposition  System 350 

219.  Method  of  Cutting  in  Transpositions  with  Slack 352 

220.  Standard  Method  of  Cutting  in  Transpositions 353 

221.  Method  of  Installing  Test  Connectors 253 

222.  Reversal  of  Line  Wires  by  Cutting  in  a  New  Transposition 354 

223.  Single-Pin  Transposition 355 

224.  Method  of  Cutting  in  Single-Pin  Transposition 355 

225.  First  Type  of  Phantom  Transposition 356 

226.  Second  Type  of  Phantom  Transposition 356 

227.  Third  Type  of  Phantom  Transposition 357 

228.  Phantom  Transpositions  Applied  to  the  A-B-C  System 357 

229.  Phantom  Transpositions  Applied  to  the  Standard  System 358 

230.  Construction  of  Phantom  Transpositions;   First  Type,  Standard  Method.  . .  .  359 

231.  Method  of  Cutting  Standard  Transposition  to  Change  to  the  First  Type  of 

Phantom  Transposition 359 

232.  Cleat  Wiring  in  First  Type  of  Phantom  Transposition 360 

233.  End  View  of  Cleat  Wiring 360 

234.  Construction  of  Phantom  Transposition;   First  Type,  Single-Pin  Method. .  .  .  361 

235.  Construction  of  Phantom  Transposition;    First  Type,   where  No  Previous 

Transposition  Existed 362 

236.  Construction  of  Phantom  Transposition,  Second  Type 363 

237.  Construction  of  Phantom  Transposition,  Third  Type 364 

238.  Single  Exposure  of  Telephone  Circuit  to  Power  Circuit 365 

239.  Unbalanced  Exposure  of  Telephone  Line  to  Power  Lines 366 

240.  Method  of  Balancing  the  Exposures  Shown  in  Fig.  239 366 

241.  General  Type  of  Balanced  Exposure 367 

242.  Transposition  of  Three- Wire  Three-Phase  Line 368 

243.  Magneto  Test  Set .' 373 

244.  Test  Set  Generator 373 

245.  Alternating  Current  Buzzer 373 

246.  Wiring  of  Lineman's  Test  Set 374 

247.  Voltmeter  Connection  for  Measuring  Line  Resistance 376 

248.  Bridge 377 

249.  Wire  Connectors 378 

251.  Wheatstone  Bridge  Circuit 379 

252.  Wheatstone  Bridge  Connection  for  Measuring  Resistance  of  Single  Line  Wire.  381 

253.  Bridge  Connection  for  Measuring  Line  Loop  Resistance 381 

254.  Connection  for  First  Measurement  in  Varley  Loop  Test 383 

255.  Connection  for  Second  Measurement  in  Varley  Loop  Test 383 

256.  Connection  for  Second  Measurement  in  Murray  Loop  Test 385 

257.  Murray  Loop  Test,  Using  Resistance  Boxes 385 

258.  Connection  for  Measurement  when  Resistance  of  Fault  is  Constant 386 

259.  First  Connection  in  Varley  Loop  Measurement  for  Crosses 387 

260.  Second  Connection  in  Varley  Loop  Measurement  for  Crosses 387 

261.  Second    Connection    in    Varley   Loop   Test    for   Locating    High-Resistance 

Crosses 388 

262.  Connection  for  Second  Measurement  of  Variable  Resistance  Crosses 389 

263.  Theoretical  Connection  for  Capacity  Test 390 

264.  Connection  for  Locating  Break  in  Line  Wire  by  Capacity  Test 391 

265.  Form  of  Pole  Line  Record 395 

266.  Form  of  Pole  Test  Panel  Record 395 

267.  Test  Panel  Wiring 396 

268.  Wiring  of  Lineman's  Telephone  Set  at  Test  Station 397 

269.  Illustration  of  the  Use  of  Patches 398 

270.  Construction  of  Shreeve  Repeater 404 

271.  Circuits  of  Shreeve  Repeater 408 


Toll  Telephone  Practice 


CHAPTER  I 
INTRODUCTION 

THE  enormous  expansion  in  the  use  of  the  telephone  in  America, 
dating  from  the  contemporaneous  inventions  of  Alexander  Graham 
Bell  and  Elisha  Gray  in  1876,  down  to  the  present  development  of 
some  8,000,000  stations,  is  a  matter  of  open  history.  Immediately 
succeeding  the  discoveries  of  Bell  and  Gray,  there  was  a  period  of 
struggle  to  open  the  way  for  commercial  development,  which  advanced 
but  slowly  up  to  1895.  The  entire  art  during  those  two  decades  was 
in  the  control  of  the  monopoly  interests  which  acquired  the  funda- 
mental patents.  It  was  necessary,  in  establishing  telephone  com- 
munication on  a  commercial  basis,  to  develop  the  art  and  at  the  same 
time  educate  the  public  to  a  realization  of  its  great  usefulness  and 
economic  value.  That  the  development  advanced  slowly  during  the 
first  decade  was  natural  and  to  have  been  expected;  that  it  did  not 
advance  more  rapidly  in  the  second  decade  is  attributable  in  part  to 
the  lack,  of  competitive  stimulation. 

At  the  opening  of  the  third  decade,  about  1895,  the  fundamental 
patents  were  expiring  and  the  field  was  thrown  open  to  competition. 
That  phase  of  the  commercial  development  which  really  commands 
amazement  began  at  this  time  and  the  succeeding  yearly  expansion 
increased  at  a  rate  not  anticipated  even  by  the  most  optimistic  fore- 
casts. The  rate  of  growth  at  the  present  time  appears  to  be  unchecked 
and  a  state  of  development  approaching  saturation  is  unquestionably 
beyond  the  immediate  future. 

The  independent  or  competitive  interests  which  entered  the  field, 
at  the  period  just  mentioned,  share  the  credit  with  the  Bell  companies 
for  the  technical  development  of  the  art;  and  to  their  efforts  is  due 
about  one-half  of  the  present  commercial  development,  in  the  number 
of  stations.  Their  influence  has  been  felt  least,  perhaps,  in  the  New 


2  TOLL  TELEPHONE  PRACTICE 

England  and  Eastern  States,  while  in  the  middle  West  they  have 
represented  a  very  large  share  of  the  whole  development  in  many 
instances.  Lacking  as  a  whole  the  benefits  of  a  strong  central  or- 
ganization or  the  extensive  support  of  large  financial  interests,  they 
have  occupied,  nevertheless,  a  most  prominent  part  in  spreading  the 
benefits  of  telephone  service.  The  early  Bell  development  was  con- 
fined practically  to  the  cities  and  towns,  and  to  building  up  a  toll 
system.  The  independent  companies  brought  about  a  marked  change 
in  this  respect,  owing  to  the  demands  for  service  in  large  numbers 
of  undeveloped  territories.  Financed  by  local  capital  and  managed 
by  local  interests  in  most  cases,  they  commenced  at  once  to  develop 
the  smaller  cities  and  towns,  and  rural  districts  in  particular.  The 
growth  of  independent  service  spread  also  to  the  larger  towns  and 
cities  and  produced  competition,  thereby  reducing  rates  and  stimu- 
lating development.  The  exceedingly  rapid  growth  of  the  service 
during  the  past  fifteen  years  is  due  in  great  measure  to  competitive 
influences,  and  in  part,  of  course,  to  the  educational  influence  of  the 
Bell  service  prior  to  this  period.  The  adoption  of  modern  or  aggres- 
sive business  methods  in  campaigning  for  new  subscribers,  by  pro- 
gressive managements  on  both  sides,  has  also  had  an  important  influ- 
ence on  the  development;  but  such  methods,  of  course,  are  largely 
inspired  by  competition,  or  the  fear  of  it. 

It  is  hardly  necessary  to  point  out  that  the  state  of  the  telephone 
art  to-day  is  exceedingly  complex  and  no  apology  is  necessary  for 
attempting  to  present  a  comprehensive  treatment  of  some  particular 
branch  of  it.  This  is  somewhat  of  a  departure  from  previous  treat- 
ments of  telephony,  but  seems  well  warranted  under  present  conditions. 
It  has  been  recognized  for  a  long  time  that  toll  systems  are  not  merely 
an  adjunct  to  local  service,  but  an  integral  and  necessary  part  of  any 
general  system.  Isolated  local  service  has  a  value  much  impaired 
in  contrast  with  combined  local  and  toll  service;  in  fact,  the  former  is 
an  illogical  condition  of  development,  except  in  very  remote  and 
unimportant  communities,  and  must  ultimately  give  way  to  the  latter. 
Toll  service,  as  distinguished  from  local,  is  a  natural  division  of  the 
general  subject  and  seems  to  be  well  past  the  point  where  it  merits 
such  consideration  as  the  authors  have  given  it  in  this  volume. 

A  word  of  explanation  here  in  regard  to  terminology,  before  enter- 
ing upon  the  historical  phase,  seems  to  be  in  place.  Common  usage 
among  telephone  men  has  led  to  the  general  classification  of  telephone 


INTRODUCTION  3 

service  under  four  headings,  as  follows :  local,  suburban,  toll  and  long 
distance.  These  are  named  in  the  order  of  advancing  distance  or 
length  of  haul,  respectively.  The  last  three  fall  within  the  scope  of 
the  present  treatment,  inasmuch  as  they  comprise  all  that  part  of 
telephone  service  which  is  not  local,  or  exchange  service.  Any  tele- 
phone call  which  is  not  local  bears  a  special  or  toll  charge  and  broadly 
may  be  termed  a  toll  call;  hence  it  seems  proper  to  use  the  term  "toll" 
to  embrace  all  service  of  this  class,  whether  it  be  suburban,  toll,  or 
long  distance  in  the  narrow  sense.  It  is  hoped  that  this  view  of  the 
matter  will  meet  with  general  approval.  The  term' "  toll "  has  been 
employed  as  a  rule  in  its  broad  sense,  throughout  this  volume;  where 
special  usage  makes  this  impossible  the  proper  construction  will  be 
duly  apparent,  if  not  explained.  The  ordinary  meanings  of  these 
terms  are  fairly  obvious,  from  their  names;  in  Bell  practice  the  terms 
"suburban"  and  "toll"  are  often  used  synonymously,  but  suburban 
business  is  always  short  haul,  comparatively,  while  toll  business  may 
be  long  haul  but  not  exceeding  100  miles.  The  term  "long  dis- 
tance" in  Bell  practice  implies  any  haul  exceeding  100  miles  and  in 
many  cases  the  toll  and  the  long  distance  business  are  handled  at 
different  switchboards,  particularly  in  the  larger  cities.  The  terms 
"toll"  and  "long  distance"  do  not  have  this  distinction  in  independ- 
ent practice  and  are  commonly  synonymous. 

The  history  of  toll  development  contains  much  that  is  instructive 
and  of  special  interest,  from  various  standpoints.  The  idea  of  com- 
munication over  long  distances  has  always  appealed  to  man's  imagina- 
tion and  no  doubt  has  greatly  stimulated  the  interest  in  this  branch 
of  the  art. 

The  pioneer  work  was  very  largely  carried  out  by  the  Bell  com- 
panies, of  course,  because  they  enjoyed  a  monopoly  of  the  business  for 
the  two  decades  next  succeeding  the  announcement  of  the  basic  dis- 
coveries. But  the  slow  commercial  progress  postponed  any  serious 
attempts  to  establish  toll  service  until  1885.  At  the  outset  such 
service  was  in  practically  no  demand  at  all  and  the  problems  to  be 
solved  had  scarcely  been  approached.  Among  the  very  earliest 
attempts  to  converse  over  telephone  lines  of  any  considerable  length 
were  those  made  between  Boston,  Mass.,  and  Providence,  R.  I. 
The  distance  between  these  cities  is  about  40  miles  and  the  circuits 
then  employed  were  single  overhead  wires  with  earth  return.  It 
speedily  developed  that  cross  talk  was  a  commercial  barrier  to  the  use 


4  TOLL  TELEPHONE  PRACTICE 

of  more  than  one  such  line  at  a  time,  when  two  or  more  were  carried 
closely  parallel  to  each  other  on  the  same  supports,  for  such  a  distance. 

These  results  seemingly  interposed  a  barrier  to  long-distance  teleph- 
ony until  it  was  proposed  to  try  the  remedy  of  metallic  lines.  About 
this  time  a  company  was  formed  to  engage  in  furnishing  long-distance 
telephone  service,  under  certain  privileges  and  restrictions  from  the 
interests  which  owned  the  Bell  and  other  fundamental  patents.  This 
corporation  was  the  American  Telephone  and  Telegraph  Company, 
which  was  formally  organized  in  1885.  The  same  year  it  commenced 
to  build  the  first  important  long-distance  line,  between  New  York 
and  Philadelphia,  a  distance  of  90  miles.  This  line  was  built  for 
metallic  circuits  and  was  completed  in  1886.  But  the  original  diffi- 
culty again  appeared  and  only  one  metallic  Circuit  could  be  used 
commercially  at  one  time,  because  of  the  cross  talk.  The  credit  for 
overcoming  this  obstacle  to  commercial  success  belongs  very  largely, 
if  not  entirely,  to  John  A.  Barrett,  who  at  that  time  was  the  electrician 
for  the  company.  Barrett  developed,  step  by  step,  a  scheme  of 
transpositions  which  made  it  feasible  to  use  all  the  circuits  simulta- 
neously in  commercial  service.  This  marked  the  commercial  opening 
of  toll  development  and  the  building  of  toll  lines  connecting  other 
cities  was  forthwith  undertaken. 

At  the  same  time,  and  in  fact  prior  to  that  period,  independent 
investigators  had  been  attracted  to  this  field,  both  in  America  and 
abroad.  Before  the  advent  of  toll  telephone  service  the  telegraph 
was  the  only  means  of  rapid  long-distance  communication.  The 
telegraph  had  already  achieved  considerable  commercial  importance 
and  had  so  far  advanced  that  various  schemes  for  multiplexing  a 
single  wire  had  been  reduced  to  a  practical  basis.  The  next  logical 
step  was  the  discovery  of  suitable  means  for  telephoning  and  tele- 
graphing simultaneously  over  a  single  wire.  Van  Rysselberghe,  a 
Belgian,  had  invented  a  system  which  accomplished  this  result  and 
came  to  America  in*  1885  to  demonstrate  his  method  on  the  lines 
of  the  Baltimore  and  Ohio  Telegraph  Company.  Many  successful 
experiments  were  conducted  and  it  was  clearly  shown  that  telegraphic 
impulses  or  signals  could  easily  be  modified  so  as  to  become  substan- 
tially inaudible  in  the  telephone  receivers  which  were  employed  for 
simultaneous  transmission.  Among  the  successful  tests  made  at  that 
time  were  those  between  Baltimore  and  Cumberland,  Md.,  a  distance 
of  178  miles;  and  between  Coeman's,  N.  Y.,  and  Fostoria,  0.  These 


INTRODUCTION  5 

experiments  culminated  in  a  test  between  New  York  and  Chicago 
which  is  of  special  interest  historically,  as  being  without  doubt  the 
longest  circuit  actually  spoken  over  until  1893,  when  commercial 
service  was  opened  between  these  cities.  The  test  was  made  in  1886, 
between  stations  at  63  Broadway,  New  York,  and  the  Palmer  House 
in  Chicago.  The  circuit  was  metallic,  employing  the  ordinary  copper 
wires  then  in  use  and  followed  the  routes  of  the  West  Shore  Railroad 
and  the  New  York,  Chicago  and  St.  Louis  (Nickel  Plate)  Railroad. 
Simultaneous  transmission  was  successfully  carried  on,  although  the 
volume  telephonically  was  very  small  and  inadequate  for  commercial 
purposes. 

Another  independent  investigator,  Rosebrugh,  had  successfully 
anticipated  Van  Rysselberghe's  claims  in  this  country,  although  his 
efforts  had  been  directed  mainly  toward  a  system  of  duplex  telephony. 
Rosebrugh's  patents  were  disposed  of  to  the  Bell  interests  and  further 
development  of  what  is  now  known  as  the  composite  system  was 
carried  out  later  under  the  direction  of  Frank  A.  Pickernell,  who  be- 
came Engineer  of  the  American  Telephone  and  Telegraph  Company. 
In  that  work  no  method  was  found  for  ringing  over  -the  telephone 
circuit  simultaneously,  without  interference,  and  the  apparatus  was 
developed  for  simplex  or  single  morse  transmission  exclusively. 

The  discovery  of  the  well-known  phantom  circuit  principle  was  made 
by  Frank  Jacobs,  although  it  was  regarded  for  some  time  as  a  method 
of  multiplex  telephony.  Jacobs'  plan  permitted  as  many  independent 
telephone  circuits  as  there  were  wires,  in  theory,  all  of  which  were 
metallic  circuits  except  one.  Thus,  from  two  wires  he  obtained  two 
independent  circuits,  one  metallic  and  one  grounded;  from  four  wires 
he  obtained  three  metallic  circuits  and  one  grounded  circuit,  and  so 
on,  each  time  doubling  the  number  of  wires.  The  principle  is  derived 
fundamentally  from  a  balanced  Wheatstone  bridge.  Its  practical 
application  has  been  limited  to  two  cases,  one  of  which  is  the  first 
or  simplest  case  where  one  metallic  circuit  and  one  grounded  circuit 
are  derived  from  two  wires,  and  the  other  is  a  limited  use  of  the  second 
case,  in  which  three  metallic  circuits  are  derived  from  four  wires.  It 
is  one  of  the  familiar  facts  of  history  that  useful  inventions  frequently 
languish  for  some  years  before  their  commercial  importance  is  at  all 
recognized,  and  in  this  case  there  was  no  exception.  The  commercial 
use  of  the  phantom  principle  had  hardly  commenced  by  1900,  but 
has  spread  rapidly  since  that  time. 


6  TOLL  TELEPHONE  PRACTICE 

The  construction  of  commercial  toll  lines  commenced  rapidly  after 
the  successful  solution  of  the  difficulties  encountered  with  the  New 
York-Philadelphia  line.  Lines  were  completed  between  Boston  and 
New  York  and  between  New  York  and  Buffalo,  connecting  with  many 
intermediate  cities,  in  1888;  the  Chicago-Milwaukee  line  was  finished 
in  1889  and  a  line  was  extended  from  Philadelphia  to  Washington, 
D.  C.,  in  the  same  year.  Many  lines  were  built  each  year  thereafter 
and  the  development  is  still  progressing  at  the  present  time. 

One  of  the  most  important  events  was  the  opening  of  the  New 
York-Chicago  line  in  1893,  which  attracted  much  attention  and 
marked  the  arrival  of  long-distance  commercial  service  in  the  full 
sense.  This  was  the  first  instance  of  the  employment  of  heavy  copper 
line  conductors,  weighing  435  pounds  per  mile.  There  was  naturally 
much  uncertainty  over  the  outcome  of  this  pioneer  attempt  to  give 
commercial  service  between  two  cities  nearly  1000  miles  apart.  The 
success  which  attended  it  is  very  remarkable  in  view  of  the  fact  that 
there  was  little  to  rely  upon  in  the  way  of  proven  theory  and  no  great 
range  of  experience  from  which  to  deduce  empirical  results.  Service 
between  all  the  large  cities  east  of  the  Missouri  and  Mississippi  rivers 
soon  followed. 

Shortly  after  this  time,  about  1895,  the  independent  telephone 
companies  entered  the  field,  as  a  result  of  the  expiration  of  fundamental 
patents.  In  a  commercial  sense  this  event  was  of  the  most  far-reach- 
ing importance  because  it  directed  the  development  as  a  whole  into 
new  channels  and  brought  telephone  service  into  communities  which 
otherwise  would  have  gone  without  it  for  some  years  to  come,  in  some 
cases  perhaps  indefinitely.  The  independent  companies  have  built 
up  no  single  great  toll  system  as  yet,  although  there  are  a  number 
of  systems  which  reach  considerable  proportions  and  cover  several 
states.  The  independent  toll  systems  taken  as  a  whole,  and  consoli- 
dated, however,  would  constitute  a  very  comprehensive  network. 
The  contributions  to  the  art  from  independent  sources,  as  regards 
toll  practice,  relate  chiefly  to  equipment  and  operating  methods.  This 
seems  but  natural  in  view  of  their  exclusion  from  all  participation 
in  the  development  until  a  comparatively  late  stage. 

In  1898,  Barrett  produced  an  improved  transposition  system  which 
has  been  standard  ever  since,  except  for  modifications  to  permit  the 
use  of  transposed  phantom  circuits.  A  very  important  contribution 
to  this  branch  of  development  was  made  by  John  J.  Carty,  who 


INTRODUCTION  7 

described  many  of  his  researches  in  a  paper  presented  before  the 
American  Institute  of  Electrical  Engineers  in  1891.  Barrett's  im- 
proved system  has  been  widely  used  on  the  lines  of  the  American 
Telephone  and  Telegraph  Company. 

The  advances  in  cable  development  up  to  this  time  had  been  chiefly 
in  the  reduction  of  electrostatic  capacity,  which  was  made  possible 
by  the  so-called  dry-core  paper  cable.  The  conductors  employed 
hitherto  had  been  selected  largely  with  reference  to  the  needs  of  local 
service.  No.  19  Brown  and  Sharpe  gauge  had  been  adopted  and  used 
as  the  standard.  It  was  not  appreciated  until  some  years  later  that 
such  conductors  were  uneconomical  for  use  in  long  toll  circuits,  al- 
though it  was  known  that  their  efficiency  was  low.  The  practice 
abroad  advanced  more  rapidly  in  this  respect  and  the  use  of  large 
gauge  toll  cables  was  undertaken  somewhat  earlier.  At  the  present 
time  it  is  well  known  that  the  proper  gauge  of  conductors  for  toll 
cables  is  settled  by  the  characteristics  of  the  lines  of  which  they  form 
a  part,  according  to  definite  laws. 

The  year  1900  was  marked  by  the  announcement  of  Dr.  Michael 
Pupin's  method  of  improving  transmission,  by  means  of  inductance 
loading.  This  invention  is  of  immense  commercial  value  and  has 
been  widely  applied,  with  greatly  beneficial  results.  The  greatest 
relative  improvement  was  obtained  by  its  application  to  cable  circuits, 
but  material  gains  are  obtained  on  long  open-wire  lines  if  the  insula- 
tion is  kept  sufficiently  high.  It  is  a  curious  circumstance  that  Oliver 
Heaviside  suggested  the  possibility  of  inductance  loading  in  1893, 
when  pointing  out  the  benefits  of  large  inductance  under  the  assump- 
tion that  it  was  uniformly  distributed.  It  is  quite  possible  that 
Heaviside's  suggestion  was  responsible  for  the  later  discovery  of  a 
successful  method  of  artificial  loading.  Heaviside  himself,  so  far  as 
known,  never  solved  the  problem.  It  is  even  more  interesting  to 
know  that  his  suggestion  was  actually  given  a  trial  in  this  country 
before  Pupin's  work  was  announced,  but  the  trial  resulted  in  a  total 
failure  because  the  loading  coils  were  of  exceedingly  large  inductance 
and  situated  a  great  many  miles  apart  on  the  circuit.  A  contemporary 
investigator  in  this  field,  with  Pupin,  was  Dr.  George  A.  Campbell, 
who  was  working  under  the  direction  of  the  American  Telephone  and 
Telegraph  Company.  The  latter  company  acquired  Pupin's  patents 
and  an  interference  suit  between  Pupin  and  Campbell  was  subsequently 
decided  in  the  former's  favor. 


8  TOLL  TELEPHONE  PRACTICE 

One  of  the  direct  results  of  Pupin's  discovery  is  the  ability  to  con- 
struct underground  toll  lines  of  considerable  length  and  high  efficiency. 
Such  lines  are  now  operating  between  New  York  and  Philadelphia, 
New  York  and  New  Haven,  Conn.,  and  between  Chicago  and  Mil- 
waukee; other  lines  of  the  same  character  are  projected.  The  applica- 
tion to  open-wire  lines  at  first  seemed  successful,  but  a  great  difficulty 
was  encountered  in  low  insulation  during  periods  of  mist,  fog,  or  rain- 
fall. A  superior  type  of  insulator,  very  recently  produced,  has  over- 
come this  objection  and  loaded  open-wire  lines  seem  now  to  be  entirely 
successful.  The  most  recent  development  is  the  application  of  loading 
to  phantom  circuits;  the  slight  superiority  of  a  phantom  circuit  over 
its  component  physical  circuits  and  the  large  gain  due  to  loading,  re- 
sults, in  the  case  of  No.  8  B.  W.  G.  copper  circuits,  in  what  is  probably 
the  most  efficient  long-distance  circuit  ever  utilized  commercially. 
It  has  been  announced  that  such  a  circuit  will  comprise  part  of  a  New 
York-Denver  connection,  when  that  service  is  opened  to  the  public. 

Within  the  last  few  years  there  have  been  several  important  im- 
provements in  composite  systems,  due  very  largely  to  the  work  of 
J.  M.  Fell  and  W.  E.  Athearn.  In  order  to  signal  for  telephonic 
purposes  over  a  composited  circuit  it  was  formerly  necessary  to 
sacrifice  one  of  the  two  morse  circuits,  but  Fell's  composite  ringer 
has  removed  the  necessity  of  this,  by  means  of  a  high-frequency 
signalling  system.  This  improvement  results  in  a  considerable  gain 
in  wire  efficiency.  The  composite  system  was  originally  developed 
for  simplex  or  single  morse  working,  but  Athearn  found  it  feasible  to 
introduce  duplex  working  after  refining  the  composite  system  and 
developing  an  improved  duplex  equipment;  in  fact,  duplex  operation 
is  superior  to  single  working.  Quadruplex  working  is  also  feasible 
for  limited  distances.  These  developments  have  brought  the  total 
wire  efficiency  to  a  remarkably  high  point;  the  ability  to  employ  two 
wires  for  commercial  metallic  toll  service,  to  signal  back  and  forth 
between  operators  and  to  work  a  full  telegraph  duplex  on  each  wire 
without  interference,  is  indeed  a  great  achievement. 

Many  investigators  have  sought  for  a  successful  telephone  repeater, 
one  that  would  work  in  either  direction  automatically  without  regard 
to  circuit  conditions  and  preserve  the  quality  or  clearness  of  trans- 
mitted speech,  and  at  the  same  time  give  a  substantial  increase  in 
volume.  No  one  has  yet  achieved  this  result,  although  many  have 
been  partially  successful.  Probably  the  most  notable  results  have 


INTRODUCTION  9 

been  obtained  by  Herbert  E.  Shreeve,  who  developed  a  successful 
repeater  for  limited  use,  under  the  direction  of  the  American  Tele- 
phone and  Telegraph  Company.  Shreeve,  in  1905,  was  granted  a 
patent  on  a  repeater  which  has  been  in  commercial  service  and  gives 
quite  satisfactory  results  under  certain  limitations.  One  of  the 
necessary  conditions  was  a  substantial  balance,  electrically,  between 
the  outgoing  lines  on  each  side  of  the  repeater,  in  order  to  eliminate 
any  tendency  to  "  howl."  Experience  shows  that  this  repeater  is  a 
comparatively  sensitive  apparatus  and  requires  the  most  careful 
maintenance.  But  now  that  the  repeater  problem  has  actually  been 
solved  for  certain  conditions  of  service,  it  is  reasonable  to  hope  that 
future  research  will  widen  its  usefulness  materially. 

The  most  recent  developments  in  toll  cable  practice  have  made  it 
possible  to  bring  phantom  circuits  into  such  cables  without  unbalance 
or  cross  talk.  This  is  accomplished  by  forming  the  core  in  a  rather 
unusual  manner.  Twisted  pairs  are  made  up  in  the  ordinary  way  and 
then  two  such  pairs  are  twisted  together  to  form  a  phantom  circuit 
element.  These  elements  are  laid  up  in  reversed  spiral  layers  after 
the  usual  manner,  and  single  twisted  pairs  are  frequently  inter- 
spersed to  make  use  of  space  which  otherwise  would  be  wasted. 
When  physical  or  phantom  circuits  are  intended  fqr  loading,  the  re- 
quirements for  perfection  of  electrical  balance  are  particularly  severe 
and  demand  the  greatest  care  in  manufacture. 

During  this  progress  of  development  there  has  been  a  marked 
change  in  switchboard  practice  and  in  the  office  equipments  generally. 
The  latter  developments  have  appeared  gradually  and  in  fact  consti- 
tute a  long  process  of  evolution.  The  numerous  improvements  have 
been  contributed  from  many  sources  and  it  is  difficult  to  separate 
the  distinct  steps.  The  early  types  of  board  were  non-multiple 
entirely  and  equipped  throughout  with  magneto  apparatus.  The 
advent  of  automatic  lamp  signals  quickly  followed  the  introduction 
of  the  common-battery  system  in  local  service.  The  multiple  type 
of  board  appeared  somewhat  later,  in  response  to  the  need  of  operating 
flexibility  in  large  installations.  The  introduction  of  the  multiple 
board  also  made  it  possible  to  economize  operating  labor,  during  hours 
of  reduced  traffic,  to  a  much  greater  extent  than  before.  There  has 
been  a  great  change  in  keyboard  practice,  also,  of  which  the  tendency 
is  toward  more  efficient  operation  through  the  reduction  of  labor  and 
the  improvement  of  supervision. 


10  TOLL  TELEPHONE  PRACTICE 

The  contemporary  development  of  toll  test  and  morse  boards  has 
likewise  been  an  evolutionary  process.  The  early  boards  were  entirely 
of  the  cord  type  and  were  comparatively  inflexible  with  respect  to 
the  needs  of  a  large  office.  The  modern  boards  are  of  the  cordless 
type,  except  for  small  installations,  and  are  provided  with  automatic 
signals  and  means  for  supervision.  They  are  also  more  systematically 
arranged,  and  equipped  with  a  view  to  flexibility  of  layout.  The 
general  progress  in  methods  of  installation  has  likewise  been  marked, 
following  in  the  wake  of  advance  in  this  respect  in  local  office  installa- 
tions. Passing  mention  should  be  made  of  the  introduction  of  various 
labor-saving  devices,  prominent  among  which  is  the  pneumatic  ticket 
carrier.  Belt  carriers  have  been  used  to  some  extent  and  are  still 
in  service  in  a  few  instances,  but  the  latest  equipments  are  usually 
provided  with  the  pneumatic  system. 


CHAPTER  II 
RURAL  TELEPHONE  EQUIPMENT 

TELEPHONE  development  in  its  early  stages  was  confined  for  the 
most  part  to  the  cities  and  large  towns.  The  growth  in  these  com- 
munities was  so  rapid  and  required  so  much  capital  that  the  develop- 
ment of  rural  districts  did  not  commence  until  a  later  date.  At  the 
time  the  fundamental  Bell  patents  expired  the  keen  competition 
inaugurated  by  the  independent  companies  began  almost  at  once  to 
stimulate  this  important  phase  of  development. 

These  independent  companies  were  comprised,  in  a  great  number 
of  instances,  of  farmers  and  country  merchants.  As  a  result  of  their 
almost  universal  inexperience  in  building  or  operating  such  plants, 
the  construction  of  the  early  rural  systems  was  crude  in  many  respects. 
The  class  of  service  expected,  however,  was  much  below  that  necessary 
to  give  satisfaction  to  subscribers  in  urban  districts  and,  moreover,  the 
necessity  for  rigid  economy  was  frequently  imperative.  The  kind  of 
service  actually  obtained  was  usually  sufficient  to  the  needs,  at  least 
for  a  time.  Service  that  now  would  not  be  tolerated  was  then  often 
welcomed  as  of  great  benefit,  in  contrast  to  the  entire  absence  of  any 
kind  of  communication,  except  the  telegraph,  but  a  short  time  before. 

As  a  means  of  keeping  down  the  cost  of  such  plants,  the  farmers 
often  contributed  the  poles  for  line  construction,  using  native  timber 
of  many  kinds";  and  furthermore,  gave  extensively  of  their  time  to 
assist  in  the  work  of  construction.  The  cash  purchases  were  usually 
limited  to  switchboards,  wire  and  telephone  sets.  These  conditions 
contributed  to  low  cost  and  low  rates.  If  the  service  was  imperfect 
and  slow,  it  should  be  remembered  that  a  delay  of  a  few  minutes  is 
not  of  great  consequence  in  business  transactions  in  such  communities, 
where  the  stress  of  city  life  is  so  little  in  evidence. 

But  conditions  as  they  were  a  decade  ago,  have  been  undergoing  a 
marked  change,  and  the  increase  in  prosperity  among  farmers,  as  well 
as  their  greater  -enlightenment  and  experience,  have  produced  a 
demand  for  better  service.  The  present  tendency  is  toward  better 

ii 


12  TOLL  TELEPHONE  PRACTICE 

equipment  and  construction  in  most  instances.  The  early  mistakes 
necessarily  exerted  a  lingering  influence  on  the  service,  because  they 
generally  related  to  the  construction  of  the  plant  and  were  hence  too 
costly  to  be  eliminated  until  the  approach  of  the  natural  reconstruc- 
tion period. 

The  efficiency  of  a  plant  from  a  service  standpoint  is  largely  settled 
as  soon  as  the  construction  is  complete.  The  early  errors  that  were 
made  in  laying  out  and  building  these  plants,  and  their  costly  effects, 
may  be  observed  still  in  many  sections  of  the  country.  The  practice 
of  cooperative  construction  without  regard  to  proper  methods  or 
standards  is  now  widely  recognized  to  be  undesirable.  Yet  many 
hundreds  of  rural  plants  were  built  wholly  or  partly  in  this  way.  It 
was  often  the  rule,  for  example,  to  require  country  subscribers  to  build 
their  own  lines  up  to  the  boundary  of  a  restricted  exchange  area  or 
zone,  at  which  point  the  telephone  company  or  association  assumed 
the  construction  and  ownership  of  the  plant.  The  type  of  line  con- 
struction obtainable  under  this  plan  in  most  instances  was  far  below 
a  proper  standard,  owing  to  the  inexperience  of  those  who  built  such 
lines  and  the  rigid  economy  generally  practiced.  Thus  we  find  in  our 
western  country  some  very  crude  conditions,  such  for  example  as 
barbed-wire  fence  lines.  Even  when  fences  were  not  resorted  to,  the 
character  of  pole  lines  was  often  of  such  a  character  as  to  be  a  public 
inconvenience,  or  even  a  menace.  Native  timber  was  used  almost 
exclusively  and  the  bark  as  a  rule  left  on;  the  sizes  as  to  length  and 
diameter  were  extremely  irregular  in  many  cases.  Again,  the  timber 
was  sometimes  so  hard  or  so  crooked  that  linemen's  spurs  were  useless 
and  pole  climbing  as  an  art  reverted  to  old-fashioned  methods. 

In  this  connection  a  description  of  a  line  observed  by  the  authors  in 
eastern  Nebraska  may  be  of  interest.  The  timber  used  for  poles  was 
osage  hedge  and  is  not  only  excessively  crooked  but  also  very  hard. 
At  the  top  of  each  pole  was  nailed  a  loop  of  wire  which  served  in  lieu 
of  an  insulator  and  the  line  wire  was  strung  loosely  through  these 
loops.  No  apparent  attempt  had  been  made  to  avoid  trees  or  foliage, 
which  grew  up  and  around  the  line  wire  in  dense  profusion.  Whether 
the  service  over  this  line,  in  good  weather  and  bad,  was  of  a  satis- 
factory character,  will  be  left  to  the  reader's  imagination. 

Farmers  who  have  had  experience  in  the  ownership  of  these  rural 
lines  are  often  glad  to  turn  them  over  to  the  telephone  company,  at 
least  ultimately.  The  maintenance  of  poor  construction  at  a  standard 


RURAL  TELEPHONE  EQUIPMENT  13 

of  high  efficiency  is  an  expensive  matter  and  the  telephone  company 
which  succeeds  to  the  ownership  of  these  lines  will  probably  replace 
them  as  soon  as  feasible  by  standard  construction.  A  company 
making  this  change  will  naturally  use  its  toll  routes  as  far  as  feasible, 
at  least  where  toll  and  rural  lines  were  once  parallel  on  the  same  right- 
of-way.  The  need  for  entirely  new  pole  lines  may  be  confined  to 
short  stretches,  if  the  toll  route  is  followed  wherever  it  is  economical 
to  make  use  of  it.  Even  though  the  toll  line  does  not  follow  the  most 
direct  route  for  rural  distribution,  it  may  still  be  economical  to  use 
it.  This  method  of  reaching  rural  subscribers  is  resorted  to  quite 
extensively. 

When  new  lines  are  under  consideration,  the  company  will  find  it 
economical  to  make  use  of  good  construction  from  the  first,  because 
such  a  course  is  essential  not  only  to  good  service,  but  to  low  mainten- 
ance costs  as  well.  By  a  proper  policy  at  the  outset  much  subsequent 
trouble  from  dissatisfied  subscribers  will  be  avoided.  A  satisfied 
subscriber  is  the  most  efficient  publicity  agent  and  his  good  will  is 
a  matter  of  concern. 

When  the  early  rural  systems  were  built  there  was  almost  complete 
freedom  from  inductive  disturbances  of  any  kind.  Grounded  lines 
in  consequence  obtained  favor  because  of  their  economy  in  first  cost 
and  annual  charges;  that  is  the  only  reason,  in  fact,  for  employing 
them  at  all  and  they  have  made  possible  a  great  deal  of  development 
that  otherwise  could  not  have  sustained  the  rates  necessary  to  meet 
the  cost  of  service.  The  rapid  development  of  electric  light  and  power 
service,  electric  railways  and  high-tension  transmission  has  worked 
much  injury  on  telephone  service  of  such  character.  Even  at  this 
time,  however,  there  are  many  communities  where  the  service  is  not 
disturbed  by  such  influences.  But  the  tendency  is  always  toward 
complications  of  this  kind,  owing  to  encroachments  of  the  character 
just  mentioned. 

There  are  two  schemes  by  means  of  which  this  trouble  may  be  solved. 
One  is  to  make  the  entire  line  metallic;  the  other  is  to  string  the 
line  metallic  for  a  distance  well  beyond  the  disturbing  field,  where 
it  should  terminate  in  one  winding  of  a  repeating  coil,  the  two. ter- 
minals of  the  other  winding  of  the  coil  being  wired  to  ground  and  the 
single  line  wire,  respectively.  Either  of  these  schemes  will  eliminate 
the  noise  on  the  line,  but  the  latter  remedy  has  the  disadvantage  of 
reducing  the  efficiency  of  speech  transmission  due  to  the  insertion  of 


14  TOLL  TELEPHONE  PRACTICE 

the  repeating  coil,  and  should  not  be  attempted  on  a  circuit  having 
subscribers  who  are  likely  to  use  long  toll  lines.  Either  of  these 
plans  for  improving  service  will  of  necessity  involve  additional  expense ; 
but  at  the  same  time  they  are  likely  to  pay  for  themselves  in  the  long 
run  in  indirect  ways,  such  as  making  it  easier  to  get  new  subscribers 
and  toll  business,  and  reducing  maintenance  expense. 

NOMENCLATURE  OF  EQUIPMENT 

The  nomenclature  employed  in  discussing  telephone  equipment 
has  become  well  established  in  most  respects.  It  does  not  seem 
necessary  to  give  here  a  glossary  of  terms  in  common  use  among 
telephone  men;  but  in  regard  to  certain  equipment  there  has  crept 
in  some  ambiguity  of  terms  that  might  give  rise  to  misunderstanding 
if  it  were  not  explained.  It  is  quite  natural  that  local  usages  of 
terms  should  not  have  identical  meanings,  in  every  instance,  through- 
out the  country. 

The  principal  variance  in  usage  occurs  in  designating  the  three 
springs  of  a  switchboard  jack  and  the  three  conductors  or  terminals 
of  a  plug.  The  designation  which  the  authors  have  used  is  the  one 
believed  to  be  in  greatest  use;  it  is  shown  in  Fig.  i.  The  terms  "  tip," 


TIP  ^ TiR 

SLEEVE 


SLEIELVE: 

RING 


FIG.  i.  —  Standard  Plug  and  Jack  Designations. 

"ring"  and  " sleeve"  are  clearly  indicated  and  denned  in  the  figure  and 
this  usage  has  been  employed  throughout. 

In  other  respects  there  seems  to  be  no  terms  in  general  use  and 
hereafter  employed  which  are  not  well  known,  or  explained  as  they 
arise. 

Subscriber's  Instrument.  —  Telephone  sets  for  use  in  rural  lines 
should  be  chosen  from  the  instruments  especially  designed  for  this 
particular  class  of  service.  They  have  distinctive  features  and  limi- 
tations, and  it  is  not  to  be  expected  that  such  service  can  be  properly 
handled  with  any  kind  of  an  instrument.  Some  telephone  companies 
practice  false  economy  in  assigning  to  rural  lines,  instruments  which 
are  too  nearly  worn  out  or  antiquated  for  town  service,  instead  of 


RURAL  TELEPHONE  EQUIPMENT  15 

sending  them  to  the  scrap  heap.  It  is  right  and  proper  for  the  busi- 
ness managers  to  see  that  the  waste  of  material  is  no  greater  than 
necessary;  but  in  their  efforts  toward  economy  they  lose  money  for 
the  company  in  many  instances  by  operating  with  old  and  inefficient 
apparatus. 

Some  of  the  most  essential  points  to  be  provided  for  in  the  design 
of  the  rural  telephone  are  that  the  bell  should  readily  respond  to  the 
ringing  current  placed  on  the  line  by  the  operator;  that  the  instrument 
shall  be  equipped  with  a  hand  generator  of  sufficient  power  to  easily 
operate  the  switchboard  signal;  and  that  the  set  shall  talk  properly, 
i.e.  transmit  and  receive  talking  current  so  that  the  parties  at  opposite 
ends  of  any  connection  whose  length  is  within  the  probability  of  operat- 
ing conditions,  can  converse  with  ease.  These  points  are  naturally  just 
as  essential  in  all  other  telephones;  but  for  the  class  of  service  under 
consideration  they  are  much  harder  to  attain,  and  so  should  be  in- 
sisted upon  with  great  vigor.  High  quality  is  demanded  for  these 
instruments  because  the  rural  line  is  longer  and  of  poorer  construction 
than  the  city  line.  Then  again,  there  is  very  often  a  tendency  to 
overload  the  country  line  by  putting  on  as  many  as  twenty-five  or 
even  thirty  telephones,  each  one  of  which  lowers  the  talking  and 
signaling  efficiency  of  the  circuit. 

As  experience  has  proven  that  the  permanent  insertion  of  low-wound 
ringer  coils  in  series  with  the  line  gives  results  vastly  inferior  to  those 
obtained  by  the  permanent  bridging  of  high-resistance  ringers,  the 
series  telephone  will  not  be  discussed.  Several  different  types  of 
bridging  telephones  are  considered  to  be  desirable  for  rural  telephone 
service,  the  precise  choice  depending  on  local  conditions  and  the 
personal  preferences  of  the  purchaser.  The  type  of  instrument 
commonly  used  is  equipped  with  a  high-wound  ringer  and  a  standard 
four-  or  five-bar  generator.  The  number  of  magnets  in  the  latter 
depends  to  some  extent  on  the  number  of  telephones  bridged  across 
the  line;  for  as  the  number  of  instruments  is  increased  the  current 
required  to  throw  the  drop  at  the  exchange  is  correspondingly  in- 
creased, as  each  additional  telephone  provides  one  more  parallel  path 
which  the  ringing  current  must  traverse  and,  therefore,  reduces  by 
a  fractional  amount  the  current  which  passes  through  the  apparatus 
at  the  end  of  the  line. 

Wiring  of  the  calling  circuit  of  these  telephones  may  follow  either 
of  the  two  standard  methods.  In  one  type  of  set  the  apparatus  is 


16  TOLL  TELEPHONE  PRACTICE 

so  arranged  that  the  subscriber,  upon  calling  central,  will  ring  his  own 
bell;  while  in  the  other,  the  local  bell  does  not  respond.  Some  manu- 
facturers maintain  that  a  subscriber  prefers  to  hear  his  own  bell  ring 
when  calling  central;  but  general  observation  seems  to  indicate  that 
this  is  not  the  case.  The  latter  conclusion  is  based  upon  the  fact  that 
a  subscriber  will  generally  place  his  left  hand  on  the  gongs  of  the 
instrument  before  turning  the  crank  of  the  generator.  Then  there 
is  the  additional  disadvantage  that  the  unnecessary  ringing  of  the 
subscriber's  bell  furnishes  another  shunt  circuit  to  the  generator 
current,  thereby  reducing  to  a  certain  extent  the  energy  available 
for  operating  the  switchboard  signal. 

There  is  one  serious  objection  to  the  straight  bridging  instrument, 
arising  from  the  fact  that  a  subscriber  cannot  signal  the  exchange 
without  ringing  the  bell  of  every  other  subscriber  on  the  line,  thereby 
greatly  reducing  the  current  which  is  effective  in  operating  the  switch- 
board signal.  Then  again,  many  subscribers  upon  hearing  their  bells 
ring  will  go  to  the  telephone  and  listen,  making  the  telephone  con- 
servation anything  but  secret  and  materially  cutting  down  the  trans- 
mission. This  objectionable  feature  can  be  avoided  easily  by  using 
a  telephone  equipped  with  a  pulsating  current  generator  in  place  of 
the  alternating  generator  commonly  employed.  The  current  from 
such  a  generator  will  not  affect  the  ringers  on  the  line  but  will  operate 
the  drop  at  the  switchboard.  This  type  of  instrument  is  commonly 
known  as  a  "  central  checking  telephone,"  because  a  subscriber 
desiring  to  converse  with  another  station  on  the  same  line  must  first 
signal  central  and  make  his  wants  known  before  obtaining  the  service 
desired. 

Another  way  of  overcoming  this  trouble  is  by  the  introduction  of 
a  grounding  key  at  the  subscriber's  instrument  and  grounding  one 
side  of  the  drop  at  the  switchboard.  The  exact  manner  in  which  this 
principle  is  applied  can  be  explained  best  with  the  aid  of  a  circuit,  a 
conventional  diagram  of  which  is  shown  in  Fig.  2. 

The  operation  of  the  circuit  is  as  follows :  Should  a  person  at  station 
2  wish  to  call  central,  he  will  first  depress  key  Ky  which  will  disconnect 
the  generator  from  the  ring  side  of  the  line  and  connect  the  corre- 
sponding side  of  the  generator  to  ground.  Consequently  the  current 
generated  upon  turning  the  crank  will  follow  a  path  that  can  be 
traced  from  the  ground  at  the  subscriber's  instrument  through  the 
generator  to  the  tip  side  of  the  line,  and  hence  through  the  break 


RURAL  TELEPHONE  EQUIPMENT 


contact  in  the  jack  and  the  coil  of  the  line  drop  to  ground.  Thus 
the  coil  of  the  line  drop  will  be  energized,  thereby  causing  its  armature 
to  be  attracted,  lifting  the  latch  and  permitting  the  drop  shutter  to 
fall.  It  will  be  observed  that  the  other  instruments  do  not  shunt 
the  current  path  traced  in  this  circuit.  Thus  a  subscriber  may  signal 
the  exchange  without  in  any  way  informing  the  other  subscribers 
on  the  circuit  that  the  line  is  in  use.  However,  in  case  the  person  at 
station  2  desires  to  speak  with  a  station  on  the  same  line,  station  i 


CORP  CIRCUIT 


C.O.PROP 

Ifl 

FLCT^ 

r\ 

ff 

ij 

1  \ 

i 

FIG.  2.  —  Grounding-button  Telephone,  Using  One  Side  of  Metallic  Line. 

for  example,  he  can  signal  this  subscriber  without  disturbing  central 
by  turning  the  generator  crank  and  allowing  key  K  to  remain  in  its 
normal  position.  This  will  obviously  force  the  generator  current  out 
on  one  side  of  the  line,  the  other  side  serving  as  a  return  path;  and 
the  current  will  necessarily  find  a  path  through  the  ringers  in  all  the 
instruments  on  the  line.  Consequently,  with  a  proper  code  of  rings, 
stations  on  the  same  line  may  signal  each  other  direct. 

The  cord  circuits  of  a  magneto  board  used  in  a  rural  telephone 
system,  having  grounding  keys,  should  be  specially  designed  to  permit 
the  operation  of  the  clearing-out  jirop  by  the  signaling  current  which 
will  flow  over  the  tip  side  of  the  line  to  ground,  as  well  as  for  generator 
current  from  a  regular  bridging  or  series  telephone.  In  Fig.  2  the 
clearing-out  drop  is  so  arranged,  the  only  special  feature  being  the 
grounding  of  the  central  point  of  the  drop  winding.  The  current 
from  any  telephone  provided  with  a  grounding  key  will,  if  the  key  K 


i8 


TOLL  TELEPHONE  PRACTICE 


is  operated,  flow  over  the  tip  side  of  the  line  and  thence  through  one- 
half  of  the  winding  of  the  clearing-out  drop  to  ground.  Current  from 
a  regular  bridging  or  series  telephone  will  pass  through  the  entire 
winding  of  the  drop,  as  neither  side  of  the  generator  is  grounded. 
In  making  up  such  a  cord  circuit,  care  must  be  taken  to  ground  the 
drop  winding  at  exactly  the  middle  point,  since  any  great  variation 
between  the  respective  sides  of  the  line  as  regards  the  resistance  from 
the  ground  out  to  the  telephone  will  have  a  tendency  to  unbalance 
the  circuit,  thus  causing  it  to  become  noisy. 

It  might  be  well  to  give  a  word  of  caution  with  respect  to  the  in- 
stallation of  the  instruments  just  described,  inasmuch  as  they  must 
be  so  wired  that  the  generator  current  will  flow  out  over  the  tip  side 
of  the  line  when  the  ground  key  is  depressed.  If  this  requirement  is 
not  observed  it  will  be  impossible  to  signal  the  exchange.  A  circuit 
is  shown  in  Fig.  3,  in  which  the  chance  of  trouble  due  to  carelessness 


ANS.JACK 

FIG.  3.  —  Grounding-button  Telephone,  Using  Both  Sides  of  Metallic  Line. 

in  this  regard  is  eliminated;  it  is  arranged  also  for  signaling  central 
without  causing  any  bell  on  the  line  to  ring.  The  operation  of  this 
circuit  is  as  follows:  When  the  subscriber  at  station  i  wishes  to  call 
the  exchange,  he  will  first  depress  the  grounding  key  K.  This  opera- 
tion grounds  one  side  of  the  generator  and  at  the  same  time  connects 
the  other  side  to  both  the  tip  and  ring  sides  of  the  line.  Therefore 
the  current  generated  will  flow  over  both  sides  of  the  line  in  parallel, 
and  through  the  two  windings  of  the  line  drop  to  ground.  The  coils 
of  this  drop  are  so  connected  that  the  magnetic  energy  created  by  the 


RURAL   TELEPHONE   EQUIPMENT  19 

current  traversing  one-half  of  the  winding  will  be  added  to  that  of 
the  other  half,  and  thus  release  the  shutter. 

When  one  station  is  calling  another  on  the  same  line,  the  key  K  is 
left  in  its  normal  position;  and  consequently  neither  side  of  the 
generator  is  grounded,  so  that  the  current  will  flow  out  over  one  side 
of  the  line  and  return  on  the  other.  Therefore  this  current  will  find 
a  path  through  the  ringer  coils  of  each  of  the  other  instruments  on 
the  line,  as  well  as  the  line  drop.  The  latter  will  not  operate,  however, 
since  the  current  passes  around  the  core  of  the  drop  in  one  direction 
to  the  middle  point  of  the  coil,  and  thence  through  the  other  half 
of  the  winding  in  the  opposite  direction.  Thus  there  is  no  tendency 
to  draw  up  the  armature,  because  the  magnetic  effect  of  one  winding 
is  neutralized  by  that  of  the  other.  It  is  obvious,  therefore,  that 
with  this  system,  as  well  as  with  the  one  previously  described,  the 
stations  on  the  line  can  signal  one  another  without  disturbing  the 
operator. 

This  latter  scheme  has  several  advantages  over  the  arrangement 
shown  in  Fig.  2.  In  the  first  place,  no  care  need  be  taken  to  connect 
the  same  side  of  all  the  telephones  to  the  tip  side  of  the  line;  and 
secondly,  since  both  sides  of  the  line  are  worked  in  parallel  in  signaling 
the  exchange,  the  resistance  of  the  path  that  must  be  traversed  by 
the  generator  current  is  only  half  as  great  as  when  a  single  wire  is 
used.  However,  with  the  system  illustrated  in  Fig.  3,  it  is  not  practi- 
cable to  arrange  the  clearing-out  drop  in  such  a  way  that  the  subscriber 
can  give  the  operator  the  disconnect  signal  without  ringing  the  bells 
of  the  other  subscribers  on  the  line.  This  is  due  to  the  fact  that  it 
is  impossible  to  operate  a  drop  with  current  flowing  from  both  sides 
of  the  line  in  parallel  through  the  drop  windings  to  ground,  and  also 
from  one  side  of  the  line  through  the  drop  windings  in  series  to  the 
other  side  of  the  line.  The  system  must  be  arranged  for  either  one 
method  or  the  other.  Since  the  latter  plan  (Fig.  3)  will  suffice  for 
straight  bridging  and  series  telephones,  as  well  as  the  special  ones,  the 
cord  circuit  used  with  this  scheme  does  not  have  the  middle  point  of 
the  clearing-out  drop  grounded.  The  drop  is  simply  bridged  across 
the  tip  and  ring  strands  of  the  cord  circuit.  Therefore  it  is  evident 
that  with  the  system  just  described,  any  station  in  ringing  off  will 
cause  all  the  bells  on  the  line  to  respond;  but  this  will  be  of  no  special 
disadvantage,  since  the  calling-in  signal  is  the  one  in  connection  with 
which  secrecy  is  so  essential. 


2O 


TOLL  TELEPHONE  PRACTICE 


The  various  circuits  employing  the  grounding  keys  solve  the  ques- 
tion of  silent  signaling  very  nicely  where  metallic  lines  are  in  use; 
but  it  is  quite  evident  that  this  scheme  cannot  be  utilized  on  a  ground 
return  system.  In  exchanges  of  this  class  the  desired  results  are 
accomplished  by  equipping  the  instruments  with  hand  generators 
capable  of  generating  either  pulsating  or  alternating  current,  and 
keys  are  so  wired  as  to  enable  the  subscribers  at  will  to  produce  either 
kind  of  current.  The  pulsating  current  is  used  in  signaling  the 
exchange  and  the  alternating  current  for  calling  the  various  subscribers 
on  the  line  by  means  of  the  usual  code  rings.  With  this  arrangement, 
one  subscriber  upon  signaling  another  will  actuate  the  drop  at  the 
switchboard.  The  operator  can  very  readily  distinguish  a  code  ring 
from  an  office  call;  and  in  case  the  call  is  for  a  station  on  the  same 
line,  she  will  simply  restore  the  drop  and  not  answer.  To  aid  the 
operator  in  distinguishing  the  code  signals,  it  is  common  practice  to 
terminate  a  line  of  the  kind  just  described  in  a  combined  ringer  and 
drop.  The  one  inherent  disadvantage  of  the  combined  ringer  and 


FIG.  4.  —  Pulsating  and  Alternating  Current  Telephone  for  Use  on  Grounded  Line. 

drop  is  that  it  takes  up  more  of  the  available  switchboard  space  than 
the  ordinary  drop.  However,  as  an  operator  is  not  able  to  care  for 
as  many  rural  lines  as  regular  subscribers'  lines,  it  will  be  found  that 
with  the  standard  type  of  switchboard  there  is  sufficient  room  for  all 
of  this  kind  of  equipment  that  an  operator  can  properly  handle. 

In  Fig.  4  are  shown  the  circuits  of  the  telephone  instruments  and 


RURAL  TELEPHONE  EQUIPMENT 


21 


the  switchboard  end  of  the  line  for  a  system  such  as  has  been  described. 
It  will  be  noted  by  referring  to  this  circuit  that  all  the  subscriber  has 
to  do  to.  call  central  is  to  turn  the  generator  crank.  This  operation 
puts  pulsating  current  on  the  line  and  thus  energizes  the  drop,  thereby 
actuating  its  armature  and  releasing  the  shutter.  Since  the  pulsating 
current  flows  in  but  one  direction,  it  will  not  affect  the  bells  at  the 
subscribers'  instruments,  as  this  current  tends  to  pull  the  bell  armature 
in  but  one  direction.  The  bell  armature  at  a  subscriber's  station  is 
normally  biased  by  a  light  spring  in  order  to  prevent  single  taps  of 
the  bell  which  pulsating  current  might  otherwise  produce. 

Under  the  scheme  outlined  in  Fig.  4,  a  subscriber  who  desires  to  call 
a  station  on  the  same  line  will  depress  key  K  and  ring,  thereby  ringing 
the  various  bells  on  the  line  as  well  as  actuating  the  drop  at  the  ex- 
change. It  is  understood,  of  course,  that  this  scheme  is  applicable  to 
metallic  as  well  as  to  grounded  lines;  but  it  is  not  quite  as  desirable  as 
the  grounding  key  system  for  the  former,  since  subscribers  on  the  same 
line  cannot  signal  each  other  without  attracting  the  attention  of  the 
operator,  and  so  tending  to  reduce  the  number  of  rural  lines  an  oper- 
ator can  handle. 


FIG.  5.  —  American  Electric  Telephone  Company's  Switchboard  Circuit  for  Pulsating 
and  Alternating  Telephone. 

This  disadvantage  of  signaling  the  office  each  time  a  subscriber 
rings  one  of  the  other  subscribers  on  the  line  has  been  avoided  by 
the  American  Electric  Telephone  Company  in  an  arrangement  of 


22  TOLL  TELEPHONE  PRACTICE 

apparatus  as  shown  in  Fig.  5.  In  this  circuit  the  relay  R  is  so 
designed  that  it  will  be  actuated  by  pulsating  current  only.  This  is 
accomplished  by  making  the  armature  of  the  relay  so  heavy  that  its 
inertia  will  be  great  enough  to  prevent  it  from  drawing  up  when  the 
relay  coil  is  traversed  by  alternating  current,  but  responsive  at  the 
same  time  to  pulsating  current. 

.  This  design  is  possible  since  an  alternating  current  in  one  complete 
cycle  passes  from  zero  to  a  maximum  in  one  direction,  back  to  zero  and 
to  a  maximum  in  the  other  direction,  and  finally  back  to  zero  again; 
whereas  the  pulsating  current  wave  passes  from  zero  to  a  maximum 
in  one  direction  only,  the  other  half  of  the  wave  being  suppressed  at 
the  generator.  Consequently  the  core  of  the  line  relay  is  exposed  to 
a  complete  reversal  of  magnetism  for  each  cycle  of  alternating  current. 
The  pulsating  current,  on  the  other  hand,  magnetizes  the  core  of  the 
drop  in  one  direction  only  and  produces  a  magnetization  of  greater 
effective  intensity.  Now,  since  the  relay  R  in  Fig.  5  must  be  energized 
before  the  line  drop  will  be  actuated  by  the  local  battery  circuit,  the 
subscribers  in  ringing  one  another  with  alternating  current  will  not 
signal  the  exchange. 

The  Western  Electric  Company  accomplishes  the  same  results  by 
making  the  armature  of'  the  drop  exceedingly  heavy  and  placing  a  cop- 
per shell  over  the  core,  thereby  dispensing  with  the  relay.  The  latter 
method  is  undoubtedly  the  better,  since  it  avoids  the  local  battery 
circuit  and  eliminates  the  use  of  the  extra  relay  for  each  circuit. 

By  referring  to  the  circuits  thus  far  shown  and  described,  it  will  be 
noted  that  a  condenser  C  has  been  placed  in  the  receiver  circuit  of  all 
the  subscribers'  sets.  The  condenser  as  shown  is  not  needed  for  the 
satisfactory  operation  of  the  telephone,  but  is  simply  inserted  in  the 
circuit  to  guard  against  trouble.  Thus  it  is  not  uncommon  for  a 
subscriber  on  one  of  these  rural  lines  to  forget  to  hang  up  his  receiver, 
or  listen  on  the  circuit  from  motives  of  mere  curiosity.  Under  such 
conditions  it  would  be  impossible  for  the  operator  to  ring  any  of  the 
subscribers  on  the  line  if  the  condensers  were  omitted,  as  the  low 
impedance  of  the  receivers  would  shunt  the  greater  part  of  the  genera- 
tor current  and  thus  prevent  the  ringers  from  receiving  enough  current 
to  actuate  them.  However,  with  the  condenser  in  circuit,  conditions* 
are  quite  different.  The  condenser  acts  as  a  high  impedance  to  the 
low-frequency  ringing  current,  and  thus  shunts  the  ringer  but  slightly. 
Consequently,  in  case  any  subscriber  carelessly  neglects  to  hang  up 


RURAL  TELEPHONE  EQUIPMENT  23 

his  receiver  he  will  not  tie  up  the  entire  line,  as  the  operator  is  still 
in  a  position  to  signal  any  station  desired.  While  this  condenser  offers 
a  very  high  impedance  to  low-frequency  currents,  the  impedance 
offered  to  the  high-frequency  voice  currents  is  very  low.  The  con- 
densers used  for  this  purpose  are  of  low  capacity,  ranging  from  one- 
half  to  three-fifths  of  one  microfarad.  Experience  with  this  plan 
leads  practically  all  managers  who  have  tried  it  to  the  opinion  that 
its  use  is  very  beneficial.  Even  though  the  initial  expense  of  the  set 
is  slightly  increased,  its  adoption  will  more  than  pay  for  itself;  it  will 
save  the  lineman  many  a  trip  into  the  country,  and  so  will  naturally 
reduce  the  cost  of  maintenance. 

In  all  of  the  systems  thus  far  described  there  is  one'  very  serious 
disadvantage,  namely,  that  the  operator  cannot  signal  the  subscribers 
secretly,  but  must  resort  to  code  signals,  thereby  informing  all  the 
stations  on  the  line  that  one  of  the  subscribers  is  being  called.  It 
will  be  conceived  very  readily  that  the  ideal  system  would  be  one  in 
which  the  subscriber  can  signal  central,  and  vice  versa,  without  in  any 
way  notifying  the  other  subscribers  on  the  line.  This  kind  of  system 
is  feasible  when  it  is  desired  to  place  but  a  limited  number  of  subscribers 
on  the  line.  Practice  and  experience  seem  to  indicate  that  four  is 
the  maximum  number  of  telephones  that  can  be  placed  on  a  grounded 
line,  when  the  ideal  conditions  are  desired,  and  that  eight  is  the  limit 
for  a  metallic  circuit.  A  scheme  which  is  frequently  utilized  in  ac- 
complishing these  results  is  the  selective  ringing  system,  using  alter- 
nating currents  of  four  different  frequencies,  with  one  ringer  tuned  to 
respond  to  each  frequency. 

Fig.  6  shows  a  circuit  in  which  the  scheme  just  referred  to  is  utilized. 
It  will  be  noted  that  the  ringer  in  each  case  is  bridged  directly  across 
the  line;  but  since  they  are  designed  so  as  to  respond  only  to  an  alter- 
nating current  of  a  particular  frequency,  the  operator  can  readily  select 
any  subscriber  by  placing  on  the  line  ringing  current  of  the  particular 
frequency  for  which  his  ringer  was  designed.  The  frequencies  ordi- 
narily used  in  these  systems  are  33,  50,  66  and  16  cycles,  for  first, 
second,  third  and  fourth  stations,  respectively.  The  design  of  the 
ringers  is  special  to  the  extent  that  the  tapper  is  rigidly  fastened  to 
a  reed  whose  natural  period  of  vibration  corresponds  to  one  of  the 
frequencies  mentioned  above,  the  tapper  itself  being  a  weight  which 
can  be  adjusted  so  as  to  tune  the  reed  almost  exactly  to  the  period 
of  vibration  desired.  The  only  difference  between  the  several  ringers 


TOLL  TELEPHONE  PRACTICE 


is  in  the  weight  of  the  tapper,  the  low-frequency  one  having  the  heaviest 
and  the  high-frequency  one  the  lightest  weight;  the  other  two  range 
between  these.  It  has  been  found  practical,  also,  to  wind  the  low- 
frequency  ringer  to  a  resistance  higher  than  the  other  three. 


1 

j 

1 

\     ! 

'           i 

! 

i 

t 

FIG.  6.  —  Four-party  Selective  System  for  Grounded  Lines. 

The  trouble  that  has  to  be  guarded  against  most  in  this  kind  of 
system  is  interference,  which  is  the  responding  of  more  than  one  ringer 
to  any  one  frequency.  This  is  very  often  due  to  a  poor  adjustment 
of  the  ringer,  or  to  the  use  of  a  ringing  current  which  is  not  of  the 
particular  frequency  for  which  the  ringer  was  tuned,  but  some  inter- 
mediate frequency  capable  of  affecting,  to  some  extent,  two  or  more 
ringers.  Then  again,  certain  harmonics  established  in  the  generation 
of  the  ringing  current  and  superimposed  on  the  regular  ringing  wave 
might  aid  in  bringing  about  the  above-mentioned  trouble.  The 
difficulty  of  interference  due  to  harmonics  has  been  reduced  almost 
to  a  minimum  by  the  insertion  of  a  one-microfarad  condenser  in  the 
ringer  circuit  as  shown  in  Fig.  6.  It  will  be  noted  that  when  the 
receiver  is  off  the  hook  the  ringer  is  shunted  by  the  receiver  circuit. 
If  the  results  above  referred  to  in  regard  to  avoiding  trouble  are 
desired,  due  to  neglecting  to  hang  up  the  receiver,  a  second  condenser 
of  one-half  microfarad  capacity  must  be  inserted  in  the  receiver  circuit. 


RURAL  TELEPHONE  EQUIPMENT  25 

There  is  one  other  condition  of  the  same  order  as  interference,  which 
must  be  guarded  against  in  magneto  systems  of  this  type.  A  standard 
hand  generator  operated  at  the  customary  speed  will  generate  a  cur- 
rent approximating  very  closely  to  sixteen  cycles.  Consequently,  if 
the  circuit  is  not  properly  designed  a  subscriber  upon  signaling  the 
exchange  may  actuate  the  sixteen-cycle  ringer.  In  the  circuit  shown, 
this  condition  is  avoided  to  some  extent  because  the  line  drop  is  wound 
to  but  100  ohms,  and  therefore  the  generator  current  will  seek  a  path 
through  this  low-wound  drop  in  preference  to  the  path  through  the 
high-wound  ringer  and  the  condenser,  the  latter  offering  considerable 
impedance.  The  elimination  of  such  trouble  is  further  aided  by 
reducing  the  output  of  the  generators  in  the  subscribers'  sets,  and  is 
very  readily  accomplished  by  taking  off  some  of  the  magnets.  This 
reduction  of  the  voltage  of  the  generator  is  necessarily  regulated  by 
the  length  of  the  line.  However,  in  case  the  line  is  of  moderate  length 
it  is  possible  to  operate  with  only  one  magnet  on  the  generator.  Many 
circuits  working  on  this  basis  are  in  daily  use,  but  no  definite  rule  can 
be  stated  regarding  the  extent  to  which  the  output  of  the  generator 
may  be  reduced,  since  this  is  governed,  in  a  large  measure,  by  the 
individual  characteristics  of  the  line.  The  most  convenient  method 
of  ascertaining  the  best  operating  condition  in  such  a  circuit  is  by  a 
process  of  experiment  and  elimination. 

Fig.  7  shows  the  harmonic  scheme  applied  to  a  metallic  line  on 
which  eight  instruments  are  installed.  In  this  case,  ringers  of  each 
frequency  are  connected  from  both  the  tip  and  the  ring  sides  of  the 
line  to  ground;  and  consequently  we  have  a  line  on  which  eight 
telephones  are  operated,  each  of  which  is  rung  selectively.  In  case  it 
is  expedient  to  place  more  than  eight  telephones  on  the  line,  a  semi- 
selective  system  can  be  resorted  to  and  sixteen  telephones  may  be 
installed.  In  this  system  four  telephones  of  each  frequency,  sixteen 
in  all,  are  bridged  across  the  line,  and  the  ringers  of  two  instruments 
of  each  frequency  are  connected  from  either  side  of  the  line  to  ground. 
Accordingly  two  ringers  will  respond  whenever  any  subscriber  is 
called,  and  the  stations  have  to  be  divided  so  as  to  respond  to  code 
signals  of  one  and  two  rings. 

In  the  foregoing  nothing  has  been  said  regarding  the  type  of  cord 
equipment  best  suited  for  rural  service.  It  has  been  common  practice 
for  many  years  past  to  use  a  cord  circuit  that  is  bridged  by  a  high- 
wound  drop.  This  arrangement  operates  very  nicely  where  the  two 


26 


TOLL  TELEPHONE  PRACTICE 


f 

w 


RURAL  TELEPHONE  EQUIPMENT 


lines  connected  are  of  the  bridging  type;  but  when  a  bridging  line  is 
connected  to  a  series  line,  the  parties  on  the  bridging  line  will  find  it 
difficult  to  operate  the  disconnect  signal,  as  the  low- wound  ringer  on 
the  series  line  will  shunt  out  the  high-wound  clearing-out  drop.  When 
these  conditions  exist  the  two  lines  might  be  tied  up  for  some  time 
before  the  op'erator  discovers  the  fact. 

To  overcome  these  troublesome  conditions,  a  cord  circuit  such  as 
shown  in  Fig.  8  has  been  employed  and  gives  entire  satisfaction. 


T1 


TO  OPRS. 
TEL. 


'/2M.r. 

FIG.  8.  —  Double  Supervision  Cord  Circuit. 

This  scheme,  as  indicated  by  the  diagram,  employs  a  clearing-out 
drop  for  each  end  of  the  cord.  The  condensers  A  and  B  are  usually 
of  one-half  microfarad  capacity,  or  slightly  greater,  and  therefore 
present  a  very  high  impedance  to  the  low-frequency  ringing  current 
and  cause  it  to  seek  the  easier  path  through  the  drop.  On  a  board 
equipped  with  this  type  of  cord  circuit,  there  is  no  difficulty  in  receiving 
a  disconnect  signal,  and  its  use  is  recommended  where  bridging  and 
series  lines  are  to  be  interconnected.  The  diagram  in  Fig.  9  shows 
the  means  of  connecting  a  repeating  coil  to  the  circuit.  The  con- 
densers, as  before,  are  to  force  the  ringing  current  through  the  clearing- 
out  drop.  The  "  talk- through  "  type  of  repeating  coil  can  be  used 
in  these  circuits,  as  it  is  not  desired  to  have  any  of  the  ringing  current 
pass  through  the  coil.  More  will  be  said  regarding  repeating  coils 
in  one  of  the  following  chapters. 

In  concluding  this  chapter  it  is  essential  to  emphasize  the  fact  that 
for  rural  telephone  instruments,  simplicity  in  the  construction  of  the 
parts  and  their  assembly  is  of  the  utmost  importance.  The  more 


28 


TOLL  TELEPHONE  PRACTICE 


complicated  the  wiring  and  the  apparatus  used,  the  greater  are  the 
chances  for  trouble;  and  consequently  a  heavy  maintenance  expense 
ensues,  as  well  as  many  complaints  of  poor  service.  Very  often 
complicated  apparatus  is  installed  with  the  idea  of  improving  the 
service,  while  in  fact  it  tends  to  bring  about  just  the  opposite  result. 
In  considering  the  purchase  of  telephones,  the  main  thing  is  not  the 


FIG.  9.  —  Double  Supervision  Cord  Circuit,  Using  Repeating  Coil. 

first  cost.*  It  is  far  better  to  think  of  the  frequency  with  which  the 
troubleman  will  be  called  upon  to  make  an  expensive  trip,  in  order  to 
make  perhaps  a  minor  adjustment  which  has  put  some  telephone,  or 
even  the  entire  line,  out  of  commission.  The  length  of  time  a  line 
will  be  out  of  service  due  to  trouble,  and  the  number  of  times  the 
subscribers  will  tolerate  interrupted  service  before  ordering  their  tele- 
phones removed,  are  questions  to  be  weighed  with  great  care  when 
contemplating  the  purchase  of  rural  instruments.  The  merit  of  re- 
liable efficient  service  is  a  great  factor  in  successful  operation  and 
should  be  kept  prominently  in  mind  when  purchasing  rural  equip- 
ment. The  highest  attainable  degree  of  simplicity  consistent  with 
the  class  of  service  given  is  commended  as  the  safest  policy  to  follow. 


CHAPTER  III 
TOLL  CUT-IN  STATIONS 

ALTHOUGH  the  number  of  small  towns  which  are  not  favored  with 
local  telephone  service  is  very  rapidly  diminishing  from  year  to  year, 
many  districts  may  still  be  found  throughout  the  United  States  in 
which  the  sole  means  of  telephonic  communication  consists  of  a  single 
toll  line  which  is  strung  through  the  locality.  Since  this  is  probably 
the  only  means  of  keeping  in  touch  with  the  neighboring  villages  and 
the  world  at  large,  it  will  stand  to,  reason  that  a  service  of  the  highest 
possible  efficiency  should  be  maintained.  However,  we  find  that 
many  such  toll  stations  are  nothing  more  or  less  than  a  telephone  set 
bridged  across  the  line;  and  when  we  consider  that,  in  all  probability, 
there  are  many  like  stations  on  either  side  of  any  particular  telephone, 
it  is  easily  understood  why  transmission  on  these  lines  is  often  very 
poor,  or  uncommercial.  The  bridging  of  these  numerous  instruments 
across  the  line  will  not  only  cut  down  the  transmission,  but  it  also 
destroys  the  privacy  of  the  conversation,  for  the  addition  of  each 
telephone  increases  the  probability  that  some  one  is  listening  to  the 
conversation.  To  run  a  separate  line  to  each  one  of  these  villages  is 
naturally  out  of  the  question;  but,  on  the  other  hand,  a  slight  outlay 
of  money  will,  if  properly  applied,  very  often  improve  conditions 
considerably. 

It  is  generally  conceded  that  the  transmission  on  any  line  should 
not  fall  below  a  well-defined  standard;  and,  therefore,  any  scheme 
or  device  which  tends  to  maintain  this  efficiency  is  of  great  benefit. 
The  fewer  the  telephones  that  are  bridged  on  a  line,  the  better  will  be 
the  transmission,  owing  to  the  fact  that  each  additional  telephone 
provides  another  path  for  the  voice  current.  While  the  coils  of  an 
ordinary  i  ooo-ohm  ringer  offer  a  very  poor  path  to  the  high-frequency 
voice  currents,  owing  to  their  high  impedance,  still  a  very  small  por- 
tion of  the  current  leaks  across.  When  this  shunting  effect  is  multi- 
plied fifteen  or  twenty  times,  or  more,  one  begins  to  notice  the  effect 
at  the  receiving  end  of  the  circuit.  While  this  effect  is  noticeable 

29 


30  TOLL  TELEPHONE  PRACTICE 

on  speech  currents,  it  is  much  more  in  evidence  on  the  ringing  current, 
as  the  ringer  coils  do  not  offer  nearly  as  much  impedance  to  the  low- 
frequency  ringing  current  as  that  presented  to  the  voice  current.  This 
is  why  it  is  so  difficult  to  ring  on  heavily  loaded  lines.  This  condition 
may  be  relieved  to  a  considerable  extent  by  using  higher  wound  ringers, 
which  reduce  the  amount  of  current  passing  through  each  ringer. 

Quite  often  a  considerable  amount  of  trouble  is  met,  due  to  placing 
telephone  ringers  of  widely  different  resistances  on  the  same  line.  The 
low-wound  ringer  provides  such  an  easy  path  for  the  ringing  cur- 
rent, that  the  high-wound  ringer  does  not  receive  a  sufficient  amount 
to  operate  it  satisfactorily,  if  at  all.  Care  should  be  exercised  to 
make  all  the  ringers  on  a  given  line  of  practically  the  same  resistance. 
If  the  line  is  very  long,  the  resistance  between  the  first  and  the  last 
instrument  may  have  the  same  effect  as  placing  high-  and  low-wound 
ringers  on  the  same  line;  i.e.,  the  ringer  in  the  instrument  nearest  to 
the  source  of  ringing  current  will  receive  the  major  portion  of  the 
current.  This  effect  may  be  overcome  by  placing  the  ringer  of  highest 
resistance  nearest  the  switchboard  end  of  the  line,  and  gradually 
diminishing  resistances  as  the  distance  increases,  thereby  causing 
each  ringer  to  receive  the  same  current.  While  this  may  be  bene- 
ficial so  far  as  ringing  the  telephones  on  the  lines  is  concerned,  it 
has  exactly  the  opposite  effect  when  a  station  near  the  end  of  the 
line  is  trying  to  call  central.  But  a  smaller  amount  of  current  is 
required  to  operate  a  drop  than  to  ring  a  bell  satisfactorily,  and  con- 
sequently, the  benefit  on  the  one  hand  is  not  altogether  offset  by  the 
detrimental  effect  on  the  other.  We  would  not  recommend  the  use 
of  this  scheme  except  on  very  long  lines,  where  trouble  has  been  ex- 
perienced in  reaching  the  stations  at  the  end  of  the  line. 

When  the  line  extends  through  trees,  the  wires  should  not  touch 
any  of  the  branches  or  even  the  foliage,  as  each  leaf  —  especially  in 
damp  weather  —  offers  a  bypath  through  which  the  line  current  may 
leak  to  ground.  On  a  long  line  on  which  the  construction  is  not  abso- 
lutely first  class,  it  will  be  noted  that  the  transmission  is  often  poorer 
in  damp  than  in  dry  weather.  This  is  caused,  to  a  certain  extent, 
by  a  very  small  amount  of  current  which  leaks  down  each  insulator. 
Furthermore,  any  foliage  that  touches  the  line  wire,  or  any  other 
defective  construction,  will  likewise  aid  in  this  diffusion  of  telephonic 
current.  If  these  conditions  are  allowed  to  multiply  to  an  extreme, 
the  combined  effect  is  often  great  enough  to  render  a  line  inoperative 


TOLL  CUT-IN  STATIONS 


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32  TOLL  TELEPHONE  PRACTICE 

in  damp  weather,  over  which  commercial  transmission  is  possible  in 
dry  weather. 

One  method  of  improving  this  rural  toll  service,  and  avoiding  to 
some  extent  the  conditions  just  outlined,  is  to  cut  off  that  portion 
of  the  line  which  is  not  actually  required  in  completing  a  connection. 
For  example,  in  Fig.  10,  suppose  a  person  at  station  4  desires  to  con- 
verse with  a  person  at  station  7.  It  will  be  apparent  that  that  por- 
tion of  the  line  which  connects  stations  number  i,  2  and  3  could  be 
disconnected  from  the  main  line  to  the  betterment  of  the  service. 
This  would  not  only  improve  the  transmission,  but  would  also  elimi- 
nate the  possibility  of  interruption  by  any  of  the  first  three  stations, 
since  they  would  be  temporarily  cut  off  from  this  part  of  the  circuits. 
The  commercial  efficiency  of  the  line  would  be  further  improved,  as 
any  two  of  the  first  three  stations  could  maintain  an  entirely  distinct 
and  separate  conversation  on  their  end  of  the  line. 

There  are  several  methods  of  accomplishing  the  above-mentioned 
results.  One  of  these  which  is  most  widely  known  is  the  method 
of  employing  a  "  cut-in  "  station,  or  "  Waterloo  equipment/'  as  it  is 
sometimes  called.  The  name  "  Waterloo  "  is  derived  from  a  town  of 
that  name  in  the  state  of  Iowa,  where  this  type  of  equipment  was  first 
used.  This  equipment  consists  of  a  box  about  the  size  of  an  ordinary 
extension  bell  box;  and  is  most  commonly  equipped  with  three  jacks, 
a  bell  and  a  cord  and  plug.  A  diagram  of  the  circuit  for  this  scheme 
is  depicted  in  Fig.  1 1 ;  from  which  it  will  be  observed  that,  normally, 
the  line  is  connected  through,  with  the  bell  B  bridged  across  the  line. 
The  operation  of  the  circuit  is  as  follows.  When  the  station  receives 
the  proper  code  of  rings,  the  subscriber  will  insert  the  plug  in  jack  2, 
and  upon  ascertaining  from  which  direction  the  call  is  coming,  he  will 
remove  the  plug  from  the  middle  jack  and  insert  it  in  jack  3  if  the  call 
originates  from  the  "  west,"  or  in  jack  i  if  the  call  comes  from  the 
"  east."  It  will  be  noted  that  upon  withdrawing  the  plug  from  jack  2, 
the  bell  B  is  again  bridged  across  the  circuit;  and  that  it  is  cut  off 
from  the  east  or  the  west  end  of  the  line  whenever  the  plug  is  inserted 
into  jack  i  or  jack  3,  respectively.  As  a  result  of  this  condition,  it 
will  be  observed  that  in  case  the  attendant  has  plugged  into  jack  3, 
and  is  conversing  with  a  "  west  "  subscriber,  the  "  east  "  subscriber 
can  easily  call  this  station,  due  to  the  fact  that  the  bell  B  is  bridged 
across  the  circuit,  and  the  "  west  "  circuit  is  entirely  independent 
of  the  "  east  "  circuit,  due  to  the  cut-off  contacts  in  jack  3. 


TOLL  CUT-IN  STATIONS 


33 


Another  method  of  reaching  the  same  result  is  shown  in  Fig.  12. 
In  this  scheme,  as  appears  in  the  diagram,  a  two-way  key  is  employed 
in  place  of  the  cord,  plug  and  jacks  used  in  the  previously  described 


TO  TELEPHONE 


FIG.  ii.  —  "Waterloo"  Station  Equipment. 

method.  The  advantages  cited  for  the  second  method  are  the  elimina- 
tion of  plug  and  cord  troubles  and^  the  superiority  of  a  key  contact 
to  a  jack  and  plug  contact.  The  operation  of  this  circuit  consists  in 
throwing  the  key  in  one  direction  to  converse  over  the  "  west "  line, 
and  in  the  opposite  direction  to  converse  over  the  "  east "  line,  the 
bell  remaining  bridged  across  the  idle  portion  of  the  circuit.  It  will 


WEST  LINE 


[          EAST  LINE 


TO  TELErHONE 
FIG.  12.  —  Toll  Cut-in  Station  with  Key  Equipment. 

be  noted  that  this  circuit  has  no  arrangement  by  means  of  which  the 
attendant's  telephone  can  be  bridged  across  the  through  line;  and 
this  constitutes  the  principal  disadvantage  of  the  scheme,  because  in 
answering  a  call,  he  is  as  likely  to  bridge  his  set  across  the  wrong  end 
as  the  right  end  of  the  circuit.  For  calls  originating  at  such  a  cut-in 
station,  it  is  necessary  to  open  the  line  to  connect  the  attendant's 
telephone  to  the  circuit;  and  this  would  interrupt  any  conversation 
which  might  be  passing  over  the  line.  These  disadvantages  can  be 
avoided  by  reversing  the  position  of  the  bell  and  the  attendant's 
telephone,  as  shown  in  Fig.  13.  In  this  case,  the  bell  in  the  telephone 
set  is  used  in  calling  the  station. 

The  attendant  at  a  station  wired  in  accordance  with  this  modifica- 


34 


TOLL  TELEPHONE  PRACTICE 


tion  has  merely  to  remove  his  receiver  from  the  hook  to  answer  a  call, 
which  is  the  least  amount  of  work  that  can  be  demanded.  In  addition 
to  this,  the  attendant  will  operate  his  cut-off  key  as  soon  as  he  ascer- 


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TO  TEL. 
FIG.  13.  —  Approved  Method  of  Wiring  Key  Equipment  at  Toll  Cut-in  Station. 

tains  from  which  direction  the  call  originated,  thereby  disconnecting 
that  portion  of  the  line  not  in  use.  This  circuit  undoubtedly  shows 
the  ideal  arrangement  for  this  type  of  equipment. 

The  arrangements  thus  far  described  are  all  designed  for  metallic 
service;  but  since  quite  a  number  of  the  lines  through  rural  districts 
are  operated  on  a  ground  return  system,  there  is  shown,  in  Fig.  14, 


WEST  LINE 

I     1    J 

1 

EAST  LINE 

^_: 

t  

TO  TEL. 
FIG.  14.  —  Toll  Cut-in  Station  for  Grounded  Lines. 

a  circuit  for  use  on  such  systems,  which  is  a  modification  of  the  one 
shown  in  Fig.  13.  The  operation  is  identical  with  that  given  in  the 
preceding  paragraph. 

Another  method  of  wiring  a  cut-in  station  on  a  ground  return 
system  is  shown  in  Fig.  15.  This  scheme  can  be  used  only  when 
through  service  is  not  required;  but  the  attendant's  station  is  so 
equipped  that  a  conversation  can  be  carried  on  in  either  direction, 
the  part  of  the  line  not  in  use  being  cut  off.  In  this  case,  the  only 
additional  apparatus  required  is  a  double-pole,  double-throw  switch 
and  an  extension  bell.  The  switch  is  so  wired,  as  indicated  in  the 


TOLL  CUT-IN  STATIONS 


35 


figure,  that  the  subscriber's  telephone  is  connected  to  one  end  of  the 
line  and  the  extension  bell  to  the  other,  when  the  switch  is  in  one 
position;  while  conditions  are  reversed  when  the  switch  is  thrown  in 


FIG.  15.  —  Telephone  Station  Switch  for  Use  with  Two  Grounded  Lines. 

the  opposite  position.  In  the  use  of  this  scheme,  it  is  well  to  equip 
the  subscriber's  set  with  a  bell  whose  ring  can  be  distinguished  readily 
from  the  response  of  the  bell  used  on  the  extension  set,  so  that  the 
attendant  can  always  tell,  by  the  character  of  the  ring,  from  which 
direction  a  call  arrives. 

In  this  connection  we  wish  to  show  the  general  method  used  in 
connecting  a  grounded  line  extension,  or  branch  line,  to  a  metallic 


WEST  LINE 


TO  TELEPHONE 
FIG.  16.  —  Toll  Station  Switch  for  Connecting  Grounded  and  Metallic  Lines. 

toll  line,  which  necessitates  the  use  of  a  repeating  coil.  The  circuit 
used  for  this  scheme  is  presented  in  Fig.  16.  The  use  of  a  repeating 
coil  becomes  necessary  because  it  is  impossible  to  connect  a  grounded 
line  direct  to  a  metallic  line  and  still  preserve  the  advantages  inherent 


36  TOLL  TELEPHONE  PRACTICE 

in  a  metallic  line.  Thus,  if  the  grounded  line  is  connected  direct  to 
one  side  of  the  metallic  line,  it  is  evident  that  the  other  side  of  the 
metallic  line  will  have  to  be  grounded  to  complete  the  circuit  through 
the  grounded  instrument.  Hence  the  metallic  circuit  would  be  practi- 
cally transformed  into  a  grounded  circuit  for  its  entire  length,  and 
would  be  susceptible  to  all  earth  currents  and  other  disturbing  features 
common  to  grounded  lines.  The  repeating  coil,  however,  keeps  the 
metallic  and  the  grounded  lines  physically  separate,  with  no  connec- 
tion, except  inductively,  through  the  coil  windings.  This  maintains 
the  balance  of  the  metallic  line  and  greatly  reduces  the  inductive 
interferences  that  might  otherwise  exist.  The  coil  shown  in  Fig.  16 
should  be  of  the  ring-through  type,  to  permit  subscribers  on  the 
grounded  line  to  ring  through  to  the  metallic  line  and  vice  versa.  The 
key  arrangement  in  this  circuit  is  the  same  as  that  shown  in  Fig.  13. 

A  few  words  of  explanation  in  regard  to  the  construction  of  the 
two  general  types  of  repeating  coils  are  appropriate  here.  The  opera- 
tion of  a  repeating  coil  rests  upon  the  same  principles  as  those  of  a 
transformer,  in  theory.  To  obtain  an  efficient  transformer  for  heavy 
electrical  currents,  the  designer  must  know  the  frequency  and  the 
voltage  of  the  primary  current  and  also  the  voltage  and  maximum 
current  that  will  be  taken  from  the  secondary  side.  In  power  work, 
these  quantities  are  all  definite;  the  designer  has  a  problem  with 
comparatively  few  variables  and  is  able  to  design  a  highly  efficient 
apparatus.  But,  on  the  other  hand,  the  number  of  variables  in  re- 
peating coil  design  is  so  great  as  to  make  it  most  difficult  to  attain 
high  efficiency. 

The  frequencies  of  voice  currents  range  from  a  few  hundred  to 
several  thousand  cycles  per  second  and,  as  such,  complicate  the  design 
of  an  efficient  transformer.  A  repeating  coil  should  be  designed  to 
transform  most  efficiently  those  frequencies  that  are  most  vital  in 
the  transmission  of  speech;  but  no  coil  will  be  uniformly  efficient  for 
all  the  frequencies.  However,  practice  has  proven  that  a  commercial 
repeating  coil  designed  with  a  comparatively  small  amount  of  iron 
will  repeat  voice  currents  with  a  talking  efficiency  of  ninety  per  cent, 
or  slightly  more.  Such  a  coil  is  intended  for  talking  currents  only, 
as  no  consideration  has  been  given  to  the  low-frequency  ringing 

currents. 

A  coil  designed  for  repeating  both  kinds  of  current  must  naturally 
cover  a  much  wider  range,  as  the  ordinary  ringing  frequency  is  about 


TOLL  CUT-IN  STATIONS 


37 


sixteen  cycles,  while  the  frequency  of  waves  corresponding  to  vocal 
overtones  may  reach  several  thousand  cycles.  The  coil  must  be 
designed  to  transmit  the  ringing  current  efficiently  enough  to  operate 
the  bells,  and  at  the  same  time  the  voice  currents  must  be  repeated 
without  material  loss  of  energy.  A  coil  designed  for  this  double 
purpose  must  have  a  large  amount  of  iron  in  its  core  to  be  able  to 
repeat  the  ringing  current;  and  the  iron  must  be  very  soft  and  finely 
laminated  in  order  to  repeat  the  voice  currents  efficiently.  Such  a  coil, 
at  best,  is  more  or  less  of  a  compromise.  If  a  coil  for  this  purpose 
is  constructed  with  a  talking  efficiency  of  about  seventy-five  per  cent 
under  the  most  severe  conditions,  its  design  may  be  considered  good. 
If  the  junction  of  the  grounded  line  with  the  metallic  line  is  not  at 
a  point  where  a  telephone  is  desired,  the  connection  can  be  made 
through  a  repeating  coil,  as  shown  in  the  diagram  in  Fig.  17.  At 


METALLIC  TOLL  LINE 


FIG.  17.  —  Repeating-coil  Connection  Between  Metallic  and  Grounded  Lines. 

points  where  repeating  coils  are  used,  special  care  should  be  exercised 
to  obtain  good  lightning  protection,  or  a  great  amount  of  trouble  will 
arise  due  to  the  burning  out  of  the  coils. 

There  are  many  standard  forms  of  protectors  which  are  satisfactory 
for  this  kind  of  work;  and  as  the  protection  required  is  identical  with 
that  which  should  be  used  at  the  toll  station  itself,  the  following 
description  will  suffice  for  both.  These  arresters  should  contain,  for 
each  line  wire,  a  fuse,  which  will  blow  if  an  abnormal  amount  of  current 
flows  over  the  line,  and  carbon  blocks  provided  with  a  small  air  gap, 
by  way  of  which  static  or  lightning  charges  can  pass  to  ground.  The 
last-mentioned  function  of  the  arrester  is  one  of  the  most  important,  as 
the  burn-outs  on  aerial  lines  can  be  traced  frequently  to  lightning. 
These  burn-outs  can  generally  be  avoided  by  providing  a  suitable 


38  TOLL  TELEPHONE  PRACTICE 

path  of  very  low  resistance  for  the  lightning.  The  most  vital  feature 
in  all  lightning  protection  is  the  provision  of  a  satisfactory  ground 
connection,  for  without  this  the  best  of  equipment  is  of  no  avail. 
When  the  building  in  which  a  telephone  is  located  is  piped  for  water, 
ready  means  for  good  and  permanent  grounds  are  available.  But 
as  this  is  of  rather  infrequent  occurrence  in  rural  districts,  other 
means  of  securing  a  satisfactory  ground  must  be  devised.  The  ordi- 
nary ground  rod,  which  is  six  feet  long  by  one-half  inch  in  diameter, 
is  very  satisfactory  for  this  purpose  in  case  the  soil  into  which  it  is 
to  be  driven  is  naturally  moist.  However,  in  loose  sandy  soil,  a  depth 
of  six  feet  is  very  frequently  insufficient  to  insure  permanent  moist 
earth  about  the  rod.  For  this  reason,  in  localities  that  are  exception- 
ally dry,  ground  rods  are  frequently  placed  in  the  cellars  under  the 
houses.  This  is  a  very  good  way  of  obtaining  a  satisfactory  ground 
connection,  as  it  practically  lengthens  the  ground  rod  by  a  length 
equivalent  to  the  depth  of  the  cellar.  Upon  securing  a  good  ground, 
the  next  step  is  to  wire  the  same  properly  to  the  arrester.  The  wire 
used  for  this  purpose  should  be  run  in  a  direct  line,  avoiding  turns  as 
much  as  possible.  The  wire  should  never  be  contained  in  an  iron 
conduit,  as  lightning  is  oscillatory  in  nature  and  of  a  very  high  fre- 
quency. In  order  to  insure  a  permanently  good  con  tact/ the  ground 
wire  should  always  be  securely  soldered  to  the  ground  rod. 

Trouble  due  to  poor  grounds,  aside  from  the  standpoint  of  pro- 
tection, is  of  frequent  occurrence  where  the  earth  is  used  as  a  return 
for  both  the  talking  and  the  ringing  currents.  In  this  case,  consider- 
able trouble  is  frequently  experienced  in  ringing  a  station,  if  the 
telephone  is  not  properly  grounded.  Thus  a  ground  might  be  of 
such  resistance  as  not  to  greatly  diminish  the  talking  current,  but  at 
the  same  time  high  enough  to  prevent  the  passage  of  sufficient  ringing 
current.  Such  cases  of  trouble  are  extremely  annoying,  for  the  trouble- 
man  may  naturally  consider  the  ground  in  good  condition,  since  the 
line  will  transmit  the  talking  currents,  and  so  attribute  the  trouble 
to  a  defective  ringer.  Another  trouble  to  which  the  ground  is  subject 
is  " drying  out";  this  may  be  very  exasperating  to  the  subscriber, 
since  the  service  will  vary  from  day  to  day  according  to  whether  the 
soil  is  dry  or  wet.  In  other  words,  the  service  will  be  good  directly 
after  a  rainfall,  from  which  time  it  will  gradually  become  poorer  as 
the  ground  dries  out. 

Having  described  the  method  of  operation  of  the  various  kinds  of 


TOLL  CUT-IN  STATIONS 


39 


equipment  for  this  class  of  work,  there  are  several  features  to  be 
noted  in  the  arrangement  of  the  equipment  itself.  The  extra  equip- 
ment necessary  for  this  service  is  sometimes  wired  in  the  telephone 
set  itself.  This  arrangement  forms  a  very  compact  equipment,  but 
since  it  makes  the  entire  equipment  special  and  the  wiring  somewhat 
complicated,  it  is  not  very  desirable.  The  most  satisfactory  equip- 
ment for  these  stations  is  a  standard  telephone  provided  with  a  1600- 
ohm  bell,  a  four-  or  five-bar  generator  and  a  separate  box  containing 
the  necessary  "cut-in  station  "  equipment.  Such  an  equipment  using 


WEST    LINE                                  If                                       EAST   LINE 

n   i  r 

CUT  IN 
STATION 

fjTJJt 

CED 

?    ? 

,-^TT^ 


TELEPHONE 


FIG.  1 8.  —  Key-type  Equipment  at  a  Toll  Cut-in  Station. 

the  key  arrangement  is  shown  in  Fig.  18  and  that  for  the  jack  and 
plug  arrangement  in  Fig.  19. 

When  it  is  desired  to  cut  in  on  a  toll  line  which  passes  through  a 
town  where  local  service  is  given,  it  is  advisable  to  run  the  line  through 
the  local  switchboard  in  accordance  with  the  circuit  shown  in  Fig.  n. 
The  bell,  in  this  case,  is  replaced  by  an  ordinary  switchboard  drop  of 
1600  ohms;  or,  possibly,  by  a  combined  ringer  and  drop,  the  latter 
of  which  aids  the  operator  in  distinguishing  the  code  signals. 

When  the  scheme  just  outlined  is  adopted,  the  operator  at  the 
switchboard  will  answer  an  incoming  call  with  the  answering  cord  of 
one  of  her  regular  cord  circuits;  and  upon  ascertaining  the  direction 
from  which  the  call  arrives,  she  will  switch  the  plug  over  to  the  proper 
'jack  and  insert  the  calling  plug  of  the  pair  used  in  the  jack  associated 
with  the  subscriber's  line  called  for,  thus  completing  the  connection. 


TOLL  TELEPHONE  PRACTICE 


Where  only  one  or  two  toll  lines  are  to  be  cared  for  at  a  small  local 
board,  it  is  sometimes  more  convenient  not  to  have  the  toll  equipment 
in  the  board  at  all,  but  mounted  in  a  box  as  previously  described,  and 
fastened  to  the  end  of  the  switchboard  cabinet  within  easy  reach  of 
the  operator.  In  this  way  the  general  arrangement  of  the  apparatus 
in  the  board  is  not  disturbed  by  any  special  equipment;  and  the  wiring 


WEST  LINE 

E.A5T   LINE 

- 

f 

i 

I  i 

Q«0 

CUT  IN   STATION 

• 

o  o  o 

TELEPHONE 


FIG.  19.  —  Jack-type  Equipment  at  a  Toll  Cut-in  Station. 

for  the  toll  lines  can  be  of  such  size  and  insulation  as  best  suits  the 
local  conditions.  It  is  customary  to  bring  the  local  lines  into  the 
switchboard  through  a  cable;  and  if  the  toll  lines  were  carried  through 
the  same  cable,  they  might  either  pick  up  some  local  trouble,  or,  in 
turn,  introduce  some  disturbance  in  the  local  lines.  Therefore  it 
will  be  seen  that  there  are  advantages  in  keeping  the  toll  equipment 
entirely  independent  of  all  other  equipment. 

In  most  cases  it  is  necessary,  in  connecting  a  toll  line  with  a  local 
line,  to  use  a  repeating  coil.  This  is  often  true  where  the  connections 
are  made  in  small  rural  exchanges;  for  here  the  majority  of  the  local 
lines  are  of  the  grounded  type.  Where  common  battery  systems  are 
employed,  the  repeating  coil  must  always  be  used,  so  that  the  only  place 
where  it  is  not  required  is  in  connection  with  metallic  magneto  lines. 
For  connecting  with  a  through  toll  line,  it  is  customary  to  have  at 
least  one  cord  circuit  in  the  switchboard  equipped  with  such  a  coil. 


TOLL  CUT-IN  STATIONS  41 

When  a  toll  line  terminates  at  the  local  board,  it  is  sometimes  more 
convenient  to  have  the  repeating  coil  inserted  permanently  in  the 
line;  this  is  the  case  if  there  are  but  one  or  two  lines,  as  the  operator 
can  use  any  cord  in  the  board  to  complete  a  toll  connection.  In 
Fig.  20  there  is  shown  a  circuit  of  a  toll  line  which  is  somewhat  special; 
but  it  has  met  with  a  great  deal  of  favor  in  some  of  the  western  states. 
The  equipment  is  all  mounted  in  a  small  box  and  attached  to  the  end 
of  the  local  switchboard.  The  terminals  of  the  toll  line,  the  public 
telephone  and  the  generator  are  brought  to  binding  posts  on  the  out- 
side of  the  box  to  facilitate  wiring.  The  line  is  normally  connected 
to  the  public  telephone  in  the  exchange,  and  when  the  operator  hears 


TO  TOLL   LINE 


TO  GEN 


FIG.  20.  —  Wiring  of  a  Toll  Terminal  for  a  Small  Switchboard. 

the  bell  ring,  she  will  answer  by  inserting  any  of  the  answering  plugs 
in  the  jack  associated  with  this  line;  this  operation  will  connect  her 
through  the  repeating  coil  to  the  toll  line.  Then,  upon  learning  that 
a  local  subscriber  is  desired,  she  will  complete  the  call  in  the  usual 
manner.  In  case  a  party  having  no  telephone  is  desired,  he  will  be 
called  by  a  messenger  to  the  public  telephone,  in  which  case  the 
operator  will  withdraw  the  plug  from  the  toll-line  jack.  When  it  is 
desired  to  call  over  the  toll  line,  the  operator  will  simply  throw  the 
ringing  key  and  turn  the  crank  of  the  hand  generator.  With  this 
arrangement,  a  conversation  from  the  public  telephone  can  be  held 
over  the  line  direct,  thereby  avoiding  the  path  through  the  repeating 
coil  and  switchboard  cords,  which  improves  the  transmission.  The 
repeating  coil,  in  this  instance,  is  of  the  talk-through  type  only;  the 
condensers  in  the  circuit  are  used  to  divert  the  generator  current 
through  the  ringer  of  the  public  telephone  at  the  toll-line  end  and 
through  the  switchboard  drop  at  the  local  end  of  the  circuit. 


CHAPTER  IV 
TOLL  POSITIONS  AT  A  LOCAL  SWITCHBOARD 

IN  approaching  the  problem  of  toll  switchboard  equipment  it  is 
but  natural  to  start  with  the  small  exchange,  in  which  one  position 
of  the  local  board  is  given  up  to  the  handling  of  toll  calls.  Therefore 
a  study  of  the  conditions  that  warrant  an  installation  of  this  kind  of 
equipment  will  be  considered  first.  In  a  small  exchange  having  from 
five  to  ten  toll  lines,  which  are  not  very  busy,  the  installation  of  a 
separate  toll  board  is  an  unnecessary  expenditure.  These  conditions 
are  nicely  met  by  equipping  the  first  position  of  the  local  board  as 
a  toll  position.  In  case  it  is  found  that  the  toll  lines  are  not  in  service 
enough  to  keep  the  toll  operator  busy,  the  rural  lines  in  the  exchange 
can  also  be  turned  over  to  her. 


FIG.  21.  —  Toll-to-Toll  Connection  at  a  Small  Magneto  Switchboard. 

In  the  study  of  toll  circuits,  the  simple  toll-to-toll  circuit  should  be 
considered  first,  inasmuch  as  this  type  of  connection  is  necessary  in 
all  toll  work,  no  matter  how  complicated  the  other  equipment  may  be. 
In  Fig.  21  is  shown  such  a  toll- to- toll  connection  which  is  suitable 

42 


TOLL  POSITIONS   AT  A  LOCAL  SWITCHBOARD 


43 


where  there  is  no  toll-line  multiple.  The  cord  circuit  used  for  this 
class  of  service  consists,  as  shown,  of  the  two  strands  of  the  cord 
across  which  is  bridged  a  standard  high-wound  clearing-out  drop. 

How  this  position  can  best  be  equipped  depends  in  a  large  measure 
upon  the  type  of  local  board,  as  to  whether  the  same  is  multiple  or  non- 
multiple,  magneto  or  common  battery.  The  various  types  of  equip- 
ment necessary  can  best  be  explained  by  a  complete  and  distinctly 
separate  description  of  each. 

The  Magneto  Non-multiple  Board.  —  This  type  of  board  very 
seldom  reaches  an  equipment  of  more  than  six  hundred  lines;  and 
since  the  revenue  from  a  board  of  this  size  is  not  large  enough  to 
warrant  the  engaging  of  an  expert,  the  toll  equipment  should  be  so 
simply  designed  that  a  man  of  little  experience  will  have  no  difficulty 
in  keeping  it  in  working  condition.  This  requirement  is  well  fulfilled 
by  the  circuit  arrangement  shown  in  Fig.  22,  the  operation  of  which 
can  most  readily  be  explained  by  tracing  a  call  through  to  completion. 


FIG.  22.  —  Toll-to-Toll  Connection  with  Repeating  Coil. 

When  a  toll  subscriber  desires  to  call  central,  he  will  operate  his 
generator,  thereby  releasing  the  shutter  of  the  high-wound  drop  that  is 
bridged  across  his  line  by  means  of  the  series  contact  in  the  line  jack. 
The  operator  will  then  insert  the  answering  plug  of  a  pair  of  cords 
in  the  jack  and  thus  disconnect  the  drop  from  the  line.  She  will 


44  TOLL  TELEPHONE  PRACTICE 

then  operate  her  listening  key  4,  and  ascertain  the  number  of  the 
subscriber  desired.  If  the  jack  of  the  subscriber  wanted  terminates 
in  the  toll  position  or  the  one  adjoining,  the  toll  operator  will  simply 
insert  her  calling  plug  and  ring.  Should  the  two  lines  thus  connected 
be  noisy,  the  operator  may,  by  operating  the  repeating  coil  key  5,  con- 
nect the  two  lines  inductively  and  thus  reduce  to  a  minimum  any 
disturbances  that  exist,  due  to  unbalance.  This  unbalanced  condition 
is  usually  caused  by  connecting  a  toll  line  with  a  local  grounded  line, 
but  the  use  of  the  repeating  coil  is  not  necessary  where  two  metallic 
lines  are  connected.  If  the  line  of  the  called  subscriber  terminates 
in  a  distant  position,  the  need  of  a  transfer  circuit  becomes  apparent. 

It  will  be  noticed  that  in  the  transfer  circuit  shown  in  Fig.  23,  the 
toll-line  end  terminates  in  a  jack,  and  that  it  ends  in  a  plug  at  the 
local  position.  The  reason  for  this  will  be  apparent  from  the  following. 
When  the  toll  operator  finds  that  she  cannot  reach  the  jack  of  the 
subscriber  desired,  she  will  plug  -into  a  transfer  terminating  in  the 
position  at  which  that  jack  is  located.  This  operation  will  light  the 
lamps  associated  with  each  end  of  the  transfer.  She  will  then  press 
an  order  key,  the  circuit  of  which  terminates  at  the  desired  position, 
and  instruct  the  local  operator  as  to  what  number  is  desired;  this 
operator,  upon  receiving  these  instructions,  will  take  up  her  transfer 
plug  and  insert  it  in  the  jack  of  the  desired  line.  The  raising  of  the 
plug  will  operate  the  plug  switch,  and  this  will  extinguish  the  transfer 
lamps.  The  toll  operator  will  then  ring  the  station  called  for  and  the 
connection  will  be  completed.  When  the  subscribers  have  finished 
they  will  "ring  off,"  thereby  operating  the  clearing-out  drop,  which 
is  permanently  bridged  across  the  cord  circuit.  The  toll  operator 
will  then  operate  her  listening  key,  to  determine  whether  the  conver- 
sation has  been  completed,  or  whether  the  subscribers  wish  further 
service.  In  case  she  finds  that  the  subscribers  have  finished  she  will 
take  down  the  connection.  This  will  light  the  lamps  associated  with 
the  transfer  circuit  and  give  the  local  operator  a  disconnect  signal; 
she  will  then  remove  the  connection  and  thus  restore  the  apparatus 
to  its  normal  condition. 

If  a  toll  call  originates  at  the  local  position,  the  answering  operator 
will  simply  take  down  the  local  plug  and  insert  the  plug  of  one  of  the 
transfer  circuits  in  the  line  jack.  This  will  operate  the  plug  switch, 
thereby  lighting-  the  lamp  associated  with  the  transfer  at  the  toll 
position,  as  well  as  the  one  at  the  local  position.  The  toll  operator, 


TOLL  POSITIONS  AT  A  LOCAL   SWITCHBOARD 


45 


46  TOLL  TELEPHONE  PRACTICE 

upon  observing  this  lighted  lamp,  will  plug  into  the  jack  associated 
with  this  transfer  circuit,  thus  extinguishing  both  lamps,  and  will 
then  handle  the  call  in  the  regular  manner  just  described. 

A  few  words  of  comment  upon  the  advisability  of  a  plug-ended 
transfer  may  be  of  interest.  As  will  be  observed  from  the  above, 
the  toll  operator  has  absolute  control  of  the  connection;  whereas  if 
a  jack-ended  transfer  were  used,  it  would  require  the  use  of  another 
cord  circuit  in  setting  up  the  connection  at  the  local  position.  This 
would  not  only  cut  down  transmission,  but  might  also  result  in  a 
confusion  of  signals.  Furthermore,  the  local  operator  would  have 
an  opportunity  to  cut  in,  by  means  of  her  listening  key;  and  this  is 
an  important  consideration  in  a  small  exchange  where  «the  operators 
are  not  always  busy. 

At  first  glance  it  might  seem  that  the  use  of  a  repeating  coil  in  each 
cord  circuit  is  superfluous.  However,  when  one  stops  to  consider 
that  this  equipment  obviates  the  changing  of  cords  due  to  special 
conditions,  which  are  prevalent  in  small  exchanges  on  account  of 
inferior  construction,  and  that  operating  efficiency  is  thereby  increased 
with  but  small  expenditure,  the  practice  seems  to  be  well  justified. 

It  is  very  often  necessary  that  the  operator  should  be  able  to  talk 
to  each  party  separately.  In  this  case  the  circuit  should  be  equipped 
with  a  double  cut-off  key  2  and  3  as  shown  in  Fig.  2 1 .  Thus  when  an 
operator  has  a  subscriber  waiting  on  the  line  for  a  toll  connection, 
she  should  be  able  to  cut  off  that  portion  of  the  line  while  she  is  making 
arrangements  for  the  other  end  of  the  connection.  By  this  means 
she  can  avoid  all  unnecessary  interruptions  by  the  waiting  subscriber, 
and,  consequently,  can  complete  her  connections  with  much  greater 
rapidity.  Since  speed  of  operation  is  an  important  factor,  small 
additional  expense  for  such  facilities  is  a  good  investment.  The  cord 
circuit  shown  in  Fig.  22  represents  advanced  or  improved  practice, 
but  has  not  yet  been  extensively  adopted  in  rural  systems.  Fig.  23 
indicates  the  conditions  which  will  be  found  prevalent  throughout  the 
country  in  the  small  plants. 

Magneto  Multiple.  —  The  next  consideration,  in  order,  is  the 
magneto  multiple  board.  A  multiple  of  all  the  local  lines  appears 
directly  in  front  of  the  toll  operator  in  this  type  of  board,  and  hence 
the  method  of  handling  toll  calls  is  simplified  to  the  extent  that  no 
trunking  equipment  is  necessary.  The  cord  circuit  previously  ex- 
plained in  Fig.  23  can  be  adapted  very  readily  to  this  class  of  service, 


TOLL  POSITIONS  AT  A  LOCAL  SWITCHBOARD 


47 


the  only  change  necessary  being  the  addition  of  a  third  conductor. 
This  third  conductor  is  the  means  by  which  battery  is  put  on  the  sleeve 
of  the  jack  for  the  busy  test,  and  is  wired  through  a  retardation  of  ten 
ohms  to  a  battery  of  about  ten  dry  cells.  This  arrangement  of  the 
equipment  is  indicated  in  Fig.  24.  When  an  operator  plugs  into  the 
multiple,  she  puts  the  potential  of  the  negative  side  of  the  previously 
mentioned  battery  on  the  sleeve  of  the  jack;  and  hence,  if  a  toll  opera- 


FIG.  24.  —  Toll-to-Local  Connection  in  a  Magnetic  Multiple  Switchboard. 

tor  tests  a  busy  line  in  the  usual  manner,  she  completes  a  circuit 
through  the  sleeve  conductor  of  her  cord  and  the  tertiary  winding  of  the 
induction  coil  to  ground,  and  will,  consequently,  obtain  the  regular 
busy  signal.  In  case  no  test  is  obtained,  the  connection  will  be  put 
up  in  a  manner  like  that  previously  explained  for  the  non-multiple 
switchboard,  when  no  trunking  is  necessary. 

THE  NON-MULTIPLE  COMMON  BATTERY  BOARD.  — In 
connecting  a  toll  line  to  a  common  battery  local  line,  it  is  impera- 
tive that  the  connection  be  made  through  a  repeating  coil,  so  as  to 
keep  the  battery  which  feeds  the  local  line  from  sending  current  out 
on  the  toll  line.  For  this  reason  the  cord  circuit  must  be  arranged  so 
that  it  is  universal,  that  is,  adapted  both  for  toll-to-toll  and  toll- to- 


48  TOLL  TELEPHONE  PRACTICE 

local  connections,  or  otherwise  two  kinds  of  cords  will  have  to  be  in- 
stalled. It  is  advisable  whenever  possible  to  make  the  cord  circuits 
universal;  for,  since  operators  are  not  infallible,  they  are  likely  in  a 
busy  moment  (if  two  sets  of  cords  are  installed)  to  use  the  wrong 
pair  of  cords,  thus  causing  confusion  and  giving  poor  service.  Fur- 
thermore, if  an  operator  does  not  have  to  work  with  two  kinds  of 
cords  she  can  handle  a  larger  number  of  calls  per  hour. 

A  very  ingenious  method  of  accomplishing  the  above  result  is 
depicted  in  Fig.  25.  The  toll  end  of  this  circuit  is  an  exact  duplicate 
of  that  shown  in  Fig.  21;  but  the  local  end  of  the  cord  is  dissimilar 
in  the  respect  that  it  has  a  three-conductor  in  place  oft,  two-conductor 
cord,  and  the  repeating  coil  key  is  omitted  since  its  functions  are 
performed  automatically  by  means  of  the  relay  in  the  sleeve  circuit. 

The  cost  per  cord  circuit  for  such  equipment  is  a  little  more  than  for 
the  other  type;  but  due  to  the  fact  that  the  operation  is  simplified, 
less  circuits  will  be  required  and  the  equipment  for  the  position  as  a 
whole  is  not  much  more  expensive.  The  design  of  this  circuit  is  such 
that  in  its  normal  condition  it  is  arranged  for  toll-to-toll  connections 
and  therefore  the  sleeve  conductors  of  the  toll-line  jacks  are  left  open. 
The  use  of  a  repeating  coil  is  not  necessary  in  a  toll-to-toll  connection, 
if  these  lines  are  metallic.  In  case  any  of  the  lines  entering  the  ex- 
change are  ground  return  circuits,  a  toll- to- toll  cord  equipped  with  a 
repeating  coil,  such  as  was  shown  in  Fig.  22,  should  be  installed. 

Referring  to  Fig.  25,  if  a  plug  is  inserted  in  the  jack  of  a  local  line 
whose  sleeve  is  wired  to  ground,  it  is  apparent  that  this  will  complete 
a  circuit  through  the  sleeve  of  the  cord  and  the  sleeve  relay  to  battery. 
This  energizes  the  relay,  thereby  placing  the  repeating  coil  in  circuit 
and  at  the  same  time  feeds  battery  current  to  the  local  subscriber. 
For  this  sort  of  connection  the  toll  operator's  work  is  reduced  to  a 
minimum. 

If  the  local  positions  at  the  board  number  three  or  more,  however, 
it  will  be  necessary  to  transfer  all  calls,  excepting  those  for  numbers 
which  terminate  in  the  jacks  at  the  toll  position  or  the  one  adjacent. 
A  transfer  well  suited  for  this  purpose  is  shown  in  Fig.  25  and  the 
method  of  operation  is  as  follows :  Should  the  toll  operator  desire  to 
connect  a  toll  line  with  a  subscriber  whose  line  terminates  in  a  distant 
position,  she  will  plug  into  one  of  the  transfer  circuits,  the  plug  end 
of  which  is  located  at  the  position  where  the  desired  line  terminates. 
This  act  will  energize  the  relay  in  the  transfer  circuit  and  thus  light 


TOLL  POSITIONS  AT  A  LOCAL  SWITCHBOARD 


49 


50  TOLL  TELEPHONE  PRACTICE 

the  lamps  associated  with  the  transfer  at  the  toll  end  and  the  local 
end.  At  the  same  time,  the  operator  will,  by  means  of  her  order 
circuit,  instruct  the  local  operator  as  to  the  number  of  the  subscriber 
desired.  Thereupon  the  local  operator  will  insert  the  plug  of  the 
transfer  associated  with  the  lighted  lamp  in  the  required  jack,  thus 
energizing  the  differential  winding  on  the  transfer  relay;  this  will 
cause  the  armature  to  fall  back,  and  the  lamps  at  both  ends  of  the 
transfer  circuit  will  be  extinguished.  The  toll  operator  will  then  ring 
the  local  subscriber  and  the  connection  will  be  completed.  When 
the  conversation  is  finished,  the  toll  subscriber  will  "ring  down"  the 
clearing-out  drop  in  the  cord  circuit,  while  the  local  subscriber,  upon 
"  hanging  up,"  will  light  the  supervisory  lamp.  The  toll  operator 
will  then  remove  the  cords,  thus  lighting  the  transfer  lamps  and 
giving  the  local  operator  a  disconnect  signal;  the  latter  will  take 
down  the  cord  of  the  transfer.  All  apparatus  will  be  restored  then  to 
its  normal  condition.  It  will  be  observed  that  in  this  system,  as  well 
as  in  those  previously  described,  the  toll  operator  has  the  entire 
supervision  of  the  connection.  This  condition  is  an  important  one 
for  fast  service.  If  a  toll  call  originates  at  a  local  position,  the  opera- 
tor will  take  down  her  local  cord  and  replace  it  with  one  of  her  transfer 
cords,  thus  lighting  the  lamp  at  the  toll  position  associated  with  this 
transfer.  The  toll  operator  will  then  take  up  the  connection  and 
complete  it  in  the  usual  manner. 

COMMON  BATTERY  MULTIPLE  SWITCHBOARD.  — When  a 
position  at  a  common  battery  multiple  board  is  equipped  as  a  toll  posi- 
tion, the  conditions  are  somewhat  different  from  those  for  a  non- 
multiple  board,  since  it  becomes  necessary  to  test  the  multiple  jacks  to 
ascertain  whether  or  not  a  line  is  busy.  A  circuit  arranged  to  meet 
these  requirements  is  shown  in  Fig.  26;  it  illustrates  the  fact  that  as  an 
exchange  grows  and  the  local  equipment  improves,  the  local  end  of  the 
toll  cord  circuit  becomes  more  complicated.  The  toll  end  of  the  cord 
is  similar  to  that  in  Fig.  21,  whereas  the  local  end  is  radically  different; 
a  two-conductor  cord  and  a  repeating  coil  key  are  again  employed. 
The  circuit  in  its  normal  condition  is  arranged  for  toll-to-local  con- 
nections with  the  repeating  coil  in  circuit,  but  the  latter  can  be  cut  out 
of  service  by  operating  key  5;  this  operation  also  disconnects  the 
battery  from  the  tip  and  the  ring  conductors  of  the  cord  circuit  and 
thus  adapts  the  circuit  for  toll-to-toll  connections. 

The  operation  of  the  circuit  is  as  follows.     When  a  toll  subscriber 


TOLL  POSITIONS  AT  A  LOCAL  SWITCHBOARD 


_J                        J 

5 

1 

1 

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MUUT. 
OACKS 

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SEE 

1 

52  TOLL  TELEPHONE  PRACTICE 

desires  a  local  connection,  the  toll  operator  will  test  the  multiple  jack 
of  the  line  desired,  in  the  usual  manner.  If  the  line  is  not  busy,  the 
sleeve  of  the  jack  is  at  ground  potential  and  hence,  if  the  operator 
touches  the  same  with  the  tip  of  her  plug,  no  flow  of  current  can  take 
place,  because  the  tip  of  the  plug  is  at  the  same  potential;  the  latter 
condition  is  caused  by  virtue  of  the  ground  attached  to  the  winding 
of  the  retardation  coil  in  the  operator's  set,  which  connects  with  the 
tip  of  the  cord  through  the  back  contact  of  the  ring  relay.  If  the  line 
is  in  use,  however,  the  potential  of  the  sleeve  of  the  jack  will  have  been 
raised,  by  the  ring  of  the  plug  inserted,  to  that  of  the  negative  side 
of  the  battery;  and,  consequently,  if  the  toll  operator  makes  a  busy 
test,  she  will  obtain  a  flow  of  current  through  the  winding  of  the 
retardation  coil  and  will  receive  the  usual  busy  signal.  This  signal  is 
the  result  of  a  readjustment  of  the  potentials  at  the  terminals  of 
condenser  C,  which  causes  a  momentary  flow  of  current  through  the 
tertiary  winding  of  the  induction  coil;  this,  in  turn,  acts  inductively 
upon  the  secondary  winding  and  causes  a  momentary  flow  of  current 
in  the  receiver  circuit.  If  she  finds  that  the  line  is  not  busy,  she  will 
insert  the  plug  and  ring  the  subscriber.  The  insertion  of  the  plug 
will  light  the  supervisory  signal  through  the  "  make  "  contact  of  the 
ring  relay.  The  signal  will  be  extinguished  when  the  subscriber 
answers,  by  the  action  of  the  tip  relay,  the  back  contact  of  which 
opens  the  lamp  circuit. 

When  the  conversation  is  finished,  the  toll  subscriber  will  "  ring 
down  "  the  clearing-out  drop;  the  local  subscriber  will  hang  up  his 
receiver,  thereby  interrupting  the  current  in  the  tip  relay,  which  in 
turn  will  cause  the  armature  to  fall  back  and  light  the  supervisory 
lamp.  The  toll  operator  will  then  take  down  the  connections  and 
restore  the  apparatus  to  its  normal  state.  In  case  a  toll  call  originates 
at  a  local  position,  the  operator,  by  means  of  her  order  circuit,  will 
give  the  toll  operator  the  number  of  the  subscriber  calling.  Then  the 
toll  operator  will  answer  in  the  multiple,  and  the  local  operator  will 
take  down  her  connection.  The  call  will  be  handled  thereafter  in 
the  regular  manner.  If  a  toll-to-toll  connection  is  desired,  the  toll 
operator  will  merely  operate  the  repeating  coil  key  5,  plug  up  the 
connection  and  ring.  If  the  exchange  contains  any  ground  return 
lines,  toll  or  rural,  it  is  advisable  to  install  one  or  more  cord  circuits 
like  that  shown  in  Fig.  22. 

In  case  the  local  multiple  is  a  three-wire  circuit  the  transformation 


TOLL  POSITIONS  AT  A  LOCAL  SWITCHBOARD 


53 


54  TOLL  TELEPHONE  PRACTICE 

of  the  cord  from  a  toll-to-toll  to  a  toll-to-local  circuit,  and  vice  versa, 
may  be  accomplished  automatically.  This  can  be  done  by  an  ar- 
rangement of  apparatus  similar  to  that  shown  in  Fig.  25. 

Thus  far,  nothing  has  been  said  about  the  operator's  circuit.  The 
circuit  shown  in  Fig.  25  contains  a  secondary  cut-out  key  7.  It  is 
quite  important  that  each  operator's  circuit  be  equipped  with  one 
of  these  keys,  since  the  operator  is  able  by  means  of  it  to  listen  to  the 
connection  without  interfering.  By  operating  this  key,  the  secondary 
of  the  induction  coil  is  opened  and  a  retardation  coil  is  inserted  in 
series  with  the  receiver.  By  opening  the  secondary  circuit  all  the 
noises  which  may  be  picked  up  by  the  transmitter  are  prevented  from 
reaching  the  line.  Furthermore,  the  insertion  of  the  retardation  coil 
of  high  impedance  materially  cuts  down  the  shunting  effect  of  the 
operator's  telephone  set. 


CHAPTER  V 
TOLL  SWITCHING  SYSTEMS 

THE  toll  line,  in  most  instances,  is  a  trunk  line  connecting  two  or 
more  cities;  and  as  such  is  used  by  any  two  widely  separated  subscribers 
who  wish  to  communicate  with  each  other.  In  some  instances,  how- 
ever, as  shown  in  the  preceding  chapters,  a  toll  line  may  terminate 
in  a  telephone  instrument.  Such  conditions*  are  confined,  naturally, 
to  small  or  isolated  villages  where  no  local  service  is  given;  and  the 
telephone  instrument,  in  such  instances,  is  usually  installed  in  some 
place  which  is  always  accessible  to  the  public,  usually  the  general 
store  or  the  post  office. 

The  interconnection  of  toll,  trunk  and  terminal  lines  to  form  con- 
tinuous circuits  between  subscribers  who  are  not  in  the  same  local 
exchange  district  is  the  mission  of  the  toll  switchboard.  Such  a  board 
fulfills  the  same  purpose  in  toll  practice  that  the  local  board  does  in 
the  local  exchange,  namely,  the  provision  of  means  for  interconnecting 
the  various  lines  comprising  the  system. 

The  toll  board  is  somewhat  more  complicated,  however,  since  there 
are  more  conditions  to  satisfy  than  in  local  service.  In  a  city  exchange 
switchboard,  the  majority  of  connections  are  made  between  subscribers 
located  in  that  particular  city  only;  while  in  a  toll  exchange  connections 
may  be  set  up  between  two  toll  stations,  or  between  a  toll  station 
and  a  distant  subscriber,  or  a  local  subscriber  and  a  toll  station,  or 
again,  between  two  local  subscribers  in  different  towns  or  cities.  In 
addition  to  setting  up  the  connections,  an  accurate  record  must  be 
kept  of  the  names  of  the  persons  or  subscribers  using  the  line  and  the 
length  of  time  the  conversation  is  carried  on,  so  that  a  proper  charge 
can  be  made  for  the  service  rendered. 

Different  kinds  of  equipment  at  the  toll  board  are  required  for 
handling  the  several  classes  of  connections  mentioned  in  the  foregoing 
paragraph.  Consequently  we  must  expect  somewhat  complicated 
conditions  both  as  to  the  construction  and  the  operation  of  the  par- 
ticular type  of  board  which  may  be  under  consideration.  The  com- 

55 


56  TOLL  TELEPHONE  PRACTICE 

plications  are  somewhat  multiplied  by  the  various  types  of  local 
boards  with  which  connections  must  be  made.  The  local  boards  can 
be  divided  into  the  three  following  classes :  the  local  battery  or  magneto 
switchboard,  in  which  an  individual  talking  battery  is  provided  with 
each  telephone;  the  common  battery  or  central  energy  switchboard, 
in  which  the  battery  used  for  talking,  as  well  as  for  signaling,  is 
located  at  the  central  office;  and  the  automatic  switchboard,  with 
which  no  manual  operators  are  required.  Each  of  the  first  two 
general  classes  may  again  be  divided  into  two  subclasses,  namely, 
the  multiple  and  the  non-multiple  equipments.  Thus  it  is  evident 
that  there  are  five  widely  different  types  of  local  equipments  which 
must  be  taken  into  consideration  in  the  design  of  toll  switchboards. 
These  five  types  are  restated  in  tabular  form  below. 

1.  Local  battery  or  magneto  switchboards: 

(a)  Non-multiple. 

(b)  Multiple. 

2.  Common  battery  or  central  energy  switchboards: 

(a)  Non-multiple. 

(b)  Multiple. 

3.  Automatic  Switchboards. 

Although  there  are  many  different  designs  of  multiple  and  non- 
multiple  common  battery  boards,  it  will  be  found  that  their  effect  upon 
the  design  of  the  toll  board  circuits,  with  which  they  are  to  operate, 
is  not  so  great  as  might  be  supposed.  The  authors'  experience  in 
adapting  a  given  toll  equipment  to  operate  with  a  local  board  of 
different  manufacture  indicates  that  there  are  few  obstacles,  if  any, 
of  a  serious  character. 

Toll  board  equipments  can  readily  be  classified  along  different  lines 
from  those  just  given,  the  basis  being  the  kind  of  service  rather  than 
the  type  of  local  board.  The  board  may  be  designed,  first,  for  con- 
necting toll  lines  with  toll  lines,  only,  this  type  of  board  being  known 
as  the  " Through  Toll  Board",  second,  the  equipment  may  be  laid 
out  for  the  connection  of  toll  lines  with  local  lines,  this  type  being 
known  as  the  "  Toll  Terminal  Board  ";  the  third  is  the  type  of  board 
which  is  most  commonly  encountered,  being  a  combination  of  the 
two  types  just  mentioned.  Each  of  these  types  may  be  divided  again 
into  multiple  and  non-multiple  equipments.  This  classification  may 
be  tabulated  as  follows: 


TOLL  SWITCHING  SYSTEMS  57 

1.  Through  toll  board: 

(a)   Non-multiple, 
v       (b)   Multiple. 

2.  Toll  terminal  board: 

(a)  Non-multiple. 

(b)  Multiple. 

3.  Combination  through  and  terminal  board: 

(a)  Non-multiple. 

(b)  Multiple. 

Each  subdivision  of  the  last  two  groups  may  be  divided  according 
to  the  classification  given  in  the  first  table;  for  example,  the  equipment 
of  a  toll  terminal  multiple  board  depends  upon  the  type  of  local  board 
with  which  it  must  operate. 

A  through  toll  board  meets  the  requirements  where  switches  be- 
tween toll  lines  are  handled  exclusively.  A  toll  terminal  board  serves 
such  requirements  as  those  at  the  center  of  a  large  city,  but  a  com- 
bination through  and  terminal  board  meets  the  average  conditions. 
The  diagram  shown  in  Fig.  28  illustrates  the  use  of  the  three  general 
types  of  toll  equipments.  It  is  possible,  at  the  through  toll  office  A , 
to  connect  a  line  which  enters  the  office  from  any  given  direction  to  a 
line  which  leaves  it  in  any  of  the  other  three  directions.  The  real 
purpose  of  the  through  office,  as  can  be  seen  readily  from  the  diagram, 
is  to  give  the  system  flexibility  with  a  minimum  amount  of  wire 
mileage.  If  this  office  were  eliminated  it  becomes  self-evident  that 
station  B  would  require  direct  lines  to  stations  F,  /,  M,  etc.  This 
would  be  satisfactory  if  there  were  sufficient  business  between  each 
of  these  points  to  keep  such  lines  constantly  in  use.  But  direct  lines 
are  not  justified  until  the  business  exceeds  a  certain  number  of  messages 
per  day;  when  the  business  is  less  than  this  amount  it  must  be  switched 
over  tandem  circuits  by  the  most  expedient  route. 

The  use  of  all  of  these  types  of  office  equipments  is  possible,  as  a 
rule,  only  in  large  toll  systems.  The  toll  plant  of  the  American  Tele- 
phone and  Telegraph  Company  is  a  case  in  point;  this  system  com- 
prises a  very  comprehensive  network  covering  the  country  as  a  whole, 
east  of  the  Rocky  mountains. 

A  good  illustration  of  the  use  of  through  and  terminal  equipments 
may  be  cited  in  the  present  installation  at  Chicago,  111.  The  long- 
distance toll  board,  for  combined  through  and  terminal  service,  was 


58  TOLL  TELEPHONE  PRACTICE 

located  formerly  at  Morrell  Park  (southwestern  outskirts  of  city), 
but  in  1908  a  new  office  was  installed  at  Franklin  St.,  in  the  downtown 
business  district,  for  terminal  service,  and  the  old  office  was  retained 
for  through  switching.  The  Morrell  Park  office  is  about  seven  miles 
from  the  business  district  and  consequently  the  change  diminished 
the  average  length  of  switching  and  recording  trunks  very  materially; 


XCHANQE 


FIG.  28.  —  Typical  Lay-out  of  a  Toll  System. 

it  also  relieved  other  difficulties  of  an  operating  nature  which  were 
burdensome.  All  toll  lines  enter  the  through  board  at  Morrell  Park 
and  pass  thence  to  the  terminal  board  at  Franklin  St.  Under  the 
operating  plan  the  terminal  operators  answer  all  incoming  toll  calls 
and  signal  the  through  operators  when  necessary;  since  the  terminal 
business  greatly  predominates,  this  plan  is  economical.  An  exception 
occurs  in  the  case  of  terminal  business  with  Milwaukee,  Wis.,  about 
85  miles  distant,  which  is  handled  over  direct  underground  loaded 
circuits. 


CHAPTER  VI 
SMALL  TOLL  SWITCHBOARDS 

THE  methods  of  handling  toll  traffic  at  one  of  the  positions  of  a 
local  board  were  outlined  in  a  preceding  chapter.  In  many  respects 
this  is  not  as  satisfactory  as  having  the  toll  equipment  located  at  an 
entirely  separate  board,  even  though  the  toll  business  is  not  very 
heavy.  The  isolation  of  the  toll  operator  from  the  local  operators, 
especially  when  there  is  insufficient  traffic  to  keep  them  all  occupied, 
will  result,  as  a  rule,  in  better  discipline  and  better  service. 

Looking  at  this  matter  from  the  standpoint  of  the  adaptability 
of  the  equipment  to  the  service  it  is  intended  for,  it  is  evident  that 
the  toll  operator  can  work  most  effectively  at  a  board  specially  de- 
signed for  such  service  rather  than  at  a  board  where  the  toll  equipment 
must  be  so  placed  as  to  conform  in  many  respects  to  an  equipment 
designed  for  local  service.  In  the  first  place,  the  keyboard  for  a  local 
equipment  is  frequently  too  high  and  too  narrow  to  afford  proper 
space  for  a  toll  operator's  work,  and  it  becomes  necessary  to  alter 
the  equipment  in  some  respects.  Space  for  spreading  out  several 
toll  tickets,  without  obscuring  signals  or  interfering  with  keys,  is  very 
essential.  It  is  often  necessary  to  mount  the  calculagraph  on  a  floor 
standard,  at  the  operator's  side,  instead  of  in  the  keyboard. 

For  these  reasons  a  separate  toll  board  has  distinct  advantages. 
This  applies  primarily,  in  the  case  of  small  offices,  to  the  period  of 
the  day  when  the  traffic  is  considerable.  There  is  ordinarily  little 
or  no  business  from  nine  P.M.  to  seven  A.M.,  and  during  this  time  it 
is  desirable,  if  possible,  to  transfer  the  toll  calls  to  the  local  board  so 
that  only  one  operator  will  be  needed. 

This  can  be  accomplished  by  duplicating  the  toll-line  equipment 
at  each  board  and  employing  a  transfer  system  as  shown  in  Fig.  29. 
This  method  employs  multiple  jacks  and  drops  at  each  board;  during 
the  day  period  the  drop  at  the  local  board  is  cut  off  by  means  of  a 
dummy  plug  in  the  jack,  and  at  night  the  plug  is  transferred  to  the 
toll  board.  This  method  suffices  very  well  if  the  number  of  toll  lines 
is  limited,  but  becomes  cumbersome  if  the  number  is  large. 

59 


6o 


TOLL  TELEPHONE  PRACTICE 


Several  plans  are  available  in  the  latter  case.  One  of  the  preferable 
methods  is  shown  in  Fig.  30,  in  which  the  toll  line  proper  terminates 
in  the  lever  springs  of  the  key,  whose  inner  contacts  are  connected  in 
series  with  the  line  to  the  toll  board,  while  the  line  to  the  local  board 


NISjHl 

POS. 


FIG.  29.  —  Method  of  Transferring  Toll  Lines  for  Night  Service  by  Means  of  Dummy 

Plugs. 

is  connected  in  a  similar  manner  to  the  outer  springs.  Thus  the  key 
is  the  means  by  which  the  toll  line  can  be  switched  at  will  from  the 
toll  to  the  local  board  and  vice  versa.  These  switching  keys  may  be 
associated  with  the  line  drops  or  the  answering  jacks  at  the  toll  board. 


sw.  KEY 


FIG.  30.  —  Method  of  Transferring  Toll  Lines  for  Night  Service  by  Means  of  Keys. 

A  very  convenient  way  is  to  use  keys  of  the  push-button  type  mounted 
on  strips  with  the  same  spacing  as  the  line  jacks  and  either  directly 
above  or  below  the  latter.  These  strips  are  made  by  the  different 
manufacturers,  varying  in  width  from  one-half  to  one  and  one-half 
inches. 


SMALL  TOLL   SWITCHBOARDS 


6l 


Some  engineers  object  to  the  scheme  outlined  in  Fig.  30  for  the 
reason  that  it  adds  an  additional  contact  in  each  of  the  line  conductors. 
While  this  is  true  and  should  be  avoided  as  far  as  possible,  there  is 
very  little  chance  for  trouble  to  originate  in  a  well-made  key.  This 
objection  is  avoided,  however,  in  the  circuit  shown  in  Fig.  31,  in  which 


FIG.  31.  —  Method  of  Transferring  Toll  Drops  for  Night  Service  by  Means  of  Keys. 

the  talking  wires  are  in  no  way  connected  with  the  switching  device. 
An  objection  to  the  latter  design  is  the  fact  that  the  drop  which  is  not 
in  use  is  connected  to  one  side  of  the  line,  the  other  side  being  opened 
by  the  key.  But  this  difficulty  is  sometimes  more  theoretical  than 
real;  it  can  be  overcome,  however,  by  the  additional  expense  of  a  key 
with  enough  contacts  to  cut  the  idle  drop  entirely  clear  of  the  line. 

The  wiring  in  Fig.  30  is  the  easiest  to  install  as  there  are  but  the 
two  line  wires  extending  between  the  two  boards;  whereas  the  circuit 
shown  in  Fig.  31  requires,  in  addition  to  this,  two  wires  to  the  switching 
key.  But  taking  everything  into  consideration,  there  is  little  to  choose 
between  the  two  methods. 

Among  the  principal  features  to  be  observed  in  the  design  of  a  toll 
board,  exclusive  of  the  equipment,  are  wide  key  shelves,  with  plenty 
of  space  for  the  operator  to  prepare  tickets  and  do  any  clerical  work 
which  may  be  assigned  to  her;  book  stalls  for  filing  the  telephone 
directories  that  may  be  required  in  obtaining  the  telephone  number 
of  a  subscriber;  pigeon  holes  for  the  filing  of  toll  tickets,  etc. 

In  Fig.  32  is  shown  a  desirable  arrangement  of  apparatus  for  a  one- 
position  toll  board.  It  will  be  noted  that  this  board  embodies  those 
features  mentioned  in  regard  to  book  stalls,  pigeon  holes  and  wide 
key  shelves.  The  reasons  for  distributing  the  equipment,  as  shown 


62 


TOLL   TELEPHONE  PRACTICE 


in  the  figure,  should  be  explained,  since  the  relative  position  of  this 
apparatus  is  important.  It  will  be  noted  that  all  the  drops  are  located 
above  the  jacks,  in  which  position  the  operator  will  always  have  a 
clear  and  unobstructed  view  of  them.  To  show  how  the  relative 
location  of  the  drops  and  jacks  will  affect  operation,  let  it  be  assumed, 
for  example,  that  some  of  the  jacks  have  been  placed  above  the  drops. 

FACE    EQUIPMENT 


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TRUNK  LAMP 


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KEY*  PLUG-SHELF  EQUIPMENT 


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FIG.  32.  —  Jack  and  Key  Equipment  of  a  Single-position  Toll  Board. 

Then,  whenever  a  number  of  connections  have  been  put  up,  it  will 
be  apparent  that  the  cords  obscure  a  full  view  of  some  of  the  drops, 
and  therefore  the  operator  may  fail  to  see  a  signal.  It  is  also  impera- 
tive that  the  line  drops  and  jacks  be  numbered  in  a  neat  and  clear 
manner,  so  that  no  time  will  be  lost  in  locating  corresponding  drops 
and  jacks.  This  is  also  true  of  the  cord  equipments;  that  is,  each 
pair  of  cords  and  the  accompanying  clearing-out  drop  should  be  num- 
bered alike.  The  cords  are  best  numbered  by  embedding  a  number 
plate  in  the  leather  plug-shelf  directly  in  front  of  each  pair  of  cords, 
while  the  drops  should  be  numbered  in  the  usual  manner. 


SMALL  TOLL   SWITCHBOARDS  63 

In  arranging  the  key  equipment  to  suit  the  convenience  of  the 
operator,  it  should  be  kept  in  mind  that  the  keys  which  will  be  used 
most  should  be  placed  nearest  the  operator  and  vice  versa.  As  shown 
in  the  last  figure,  the  repeating  coil  key  is  the  one  nearest  the  face  of 
the  board,  because  it  is  operated  but  once,  if  at  all,  during  a  connection. 
The  double  cut-off  key  has  its  place  next  to  the  operator  and  the 
ringing  and  listening  key  is  placed  between  the  other  two.  This 
arrangement,  or  one  in  which  the  relative  positions  of  the  double  cut- 
off and  the  ringing  and  listening  keys  are  reversed,  are  the  ones  most 
generally  used. 

Although  the  equipment  shown  in  the  diagram  is  intended  for  a 
toll  board  which  is  to  work  in  connection  with  a  magneto  local  board, 
the  same  general  arrangement  of  apparatus  would  be  used  for  a 
board  that  is  to  operate  in  connection  with  a  common  battery  local 
board,  with  the  exception  that  a  supervisory  lamp  should  be  added 
for  each  cord  circuit,  this  lamp  being  placed  in  front  of  each  pair  of 
cords. 

In  Fig.  33  is  shown  the  arrangement  of  the  equipment  for  a  two- 
position  toll  board,  designed  to  operate  in  connection  with  a  common 
battery  local  board.  The  general  arrangement  of  apparatus  is  the 
same  as  for  the  one -position  board,  with  the  exception  that  the  trunk 
jacks  are  placed  in  the  middle  panel.  This  is  advisable  because  in 
that  position  they  are  more  easily  accessible  to  each  operator.  A 
calculagraph  is  placed  in  the  key  shelf  between  the  two  operators,  so 
that  toll  connections  may  be  accurately  timed. 

Managers  are  sometimes  of  the  opinion  that  the  purchase  of  a  cal- 
culagraph is  an  unnecessary  expense  for  a  small  board ;  but  experience 
has  shown  that  this  instrument  will  more  than  pay  for  itself,  because 
of  the  accuracy  with  which  calls  can  be  timed  with  little  labor,  and 
the  reduction  of  unpaid  overtime.  It  is  now  universally  acknowledged 
by  men  who  have  had  experience  with  large  toll  boards,  that  the 
calculagraph  is  indispensable  for  this  work.  If  it  is  a  profitable 
investment  for  such  boards,  it  should  be  equally  valuable  for  small 
boards  unless  the  volume  of  business  is  extremely  limited.  An  ordi- 
nary clock  is  in  no  sense  a  substitute  for  the  calculagraph  and  gives 
unsatisfactory  results. 

The  equipment  of  small  toll  boards  will  next  be  discussed  in  relation 
to  the  four  types  of  local  board  with  which  it  may  operate,  magneto 
and  common  battery,  non-multiple  and  multiple,  respectively. 


64 


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SMALL  TOLL  SWITCHBOARDS  65 

Magneto  Non-multiple  Switchboard.  —  The  circuits  used  at  a  toll 
board  which  is  to  operate  in  connection  with  a  local  magneto  non- 
multiple  switchboard  are  identical  with  those  used  at  the  toll  position 
at  the  local  board;  and,  consequently,  will  require  no  further  discussion 
in  this  chapter. 

Magneto  Multiple  Switchboard.  —  The  operation  of  a  toll  board  in 
connection  with  a  local  magneto  multiple  board  is  similar  to  that  of 
the  magneto  non-multiple  board,  the  only  difference  being  in  the  trunk 
circuit.  The  plug  at  the  local  end  of  this  circuit  must  be  provided 
with  a  sleeve  conductor  which  will  raise  the  potential  of  the  sleeve  of 
the  jack,  in  which  it  may  be  inserted  from  ground  to  that  of  the 
negative  side  of  battery,  for  the  usual  busy  test.  The  trunk  circuit 
used  for  this  purpose  will  be  identical  with  the  one  shown  in  Fig.  25, 
with  the  exception  that  the  jack  at  the  toll  board  will  be  of  the  two- 
conductor  type.  In  order  to  obtain  a  clear  conception  of  the  opera- 
tion of  this  system,  it  seems  advisable  to  trace  a  call  through  its 
complete  course. 

Upon  the  arrival  of  an  incoming  toll  call,  the  operator  after  ascer- 
taining the  number  of  the  subscriber  desired,  will  insert  the  calling 
plug  of  the  pair  of  cords  in  use  in  one  of  the  trunk  jacks,  thus  energizing 
the  relay  and  lighting  the  lamps  at  the  toll  and  the  local  ends  of  the 
trunk.  At  the  same  time,  by  means  of  her  order  circuit,  she  will 
instruct  the  local  operator  at  whose  position  the  trunk  terminates, 
as  to  the  subscriber's  number  desired;  whereupon  the  local  operator 
will  insert  the  plug  (associated  with  the  lighted  lamp)  in  the  multiple 
jack  of  the  line  called  for.  This  will  extinguish  the  lamps  at  each  end 
of  the  trunk  as  previously  described.  If  the  toll  operator,  upon 
listening,  finds  the  line  is  not  busy,  she  will  ring  the  subscriber;  in 
case  the  line  is  busy,  however,  she  will  leave  her  cut-off  key  open  until 
the  local  subscriber  is  disengaged.  It  has  sometimes  been  the  practice 
for  the  toll  operator  to  interrupt  a  local  message,  so  as  to  complete 
the  toll  connection  with  the  least  delay.  When  the  conversation  is 
finished  both  subscribers  "  ring  off,"  thereby  actuating  the  clearing- 
out  drop.  The  toll  operator  will  then  take  down  the  connections, 
thus  opening  the  circuit  of  one  of  the  differential  relay  windings,  which 
will  light  the  lamps  associated  with  the  trunk  circuit  in  use.  This 
gives  the  local  operator  a  disconnect  signal  and  she  will  then  remove 
the  connection  and  thus  restore  the  apparatus  to  its  normal  condition. 

Should  the  call  originate  at  the  local  board,  the  operator,  upon 


66  TOLL  TELEPHONE  PRACTICE 

ascertaining  that  a  toll  connection  is  desired,  will  withdraw  the  plug 
of  the  answering  cord  and  insert  the  plug  of  one  of  the  toll  trunks. 
This  will  light  the  lamp  associated  with  the  trunk  in  front  of  the  toll 
operator,  who  in  turn  will  answer  and  complete  the  connection  in  the 
usual  manner. 

Common  Battery  Non-multiple  Switchboard.  —  The  operation  of 
a  toll  board  in  connection  with  a  common  battery  non-multiple  board 
is  identical  with  that  previously  described  for  a  toll  position  located 
at  the  local  board  itself.  The  circuits  used  are  of  the  same  general 
design  as  those  shown  in  Fig.  25. 

Common  Battery  Multiple  Switchboard.  —  A  non-multiple  toll 
board  that  is  to  work  in  conjunction  with  a  common  battery  multiple 
board  is  somewhat  more  complicated,  as  one  would  naturally  expect, 
than  any  of  the  types  thus  far  considered  and  a  more  complete  de- 
scription of  its  operation  is  therefore  included. 

Although  the  toll-line  equipment  remains  the  same,  the  necessary 
methods  of  trunking  to  and  from  the  local  board  are  more  complex 
and  the  major  part  of  the  description  will  be  devoted  to  such  opera- 
tion. There  are  two  general  methods  of  handling  connections  be- 
tween the  toll  and  the  local  boards.  The  first  comprises  a  two-way 
trunk,  which  may  be  used,  as  the  name  implies,  for  putting  up  a 
connection  from  the  toll  to  the  local  board  or  vice  versa,  the  second 
employs  separate  recording  and  switching  trunks.  The  first  system 
mentioned  is  well  adapted  to  an  exchange  where  there  are  ten  positions 
or  less  equipped  at  the  local  board.  The  reasons  for  this  will  become 
apparent  after  completing  the  description.  The  circuit  used  for  such 
a  system  is  shown  in  Fig.  34,  and  reference  will  be  made  to  this  in 
tracing  out  the  following  connection. 

When  an  incoming  toll  call  is  received,  the  toll  operator  will  place 
herself  in  connection  with  the  local  board  by  means  of  her  order  circuit, 
and  instruct  the  operator  as  to  the  number  called  for.  The  local 
operator  will  then  assign  the  trunk  to  be  used  and  insert  the  plug  of 
the  latter  in  the  multiple  jack  of  the  subscriber's  line  wanted.  If  the 
local  line  is  idle,  a  circuit  may  be  traced  from  ground  by  way  of  relay 
Ej  to  the  sleeve  of  the  jack,  thence  over  the  ring  strand  of  the  trunk 
through  the  series  contact  in  the  trunk  jack  and  through  relay  A  to 
battery.  These  relays  will  consequently  be  energized  and  will  light 
the  lamp  associated  with  the  local  end  of  the  trunk,  in  case  the  toll 
operator  has  not  previously  plugged  into  the  jack.  The  act  of  plug- 


SMALL  TOLL  SWITCHBOARDS 


67 


68  TOLL  TELEPHONE  PRACTICE 

ging  into  this  jack  will  open  the  series  contacts  in  the  latter  and  thus 
de -energize  relay  A  and  extinguish  the  lamp.  At  the  same  time  a 
circuit  will  be  established  from  the  ground  at  E,  over  the  ring  strand 
of  the  trunk  and  the  toll  cord,  through  the  contacts  of  keys  i  and  2 
and  relay  C  to  battery.  This  relay,  therefore,  will  be  energized  and 
will  light  the  supervisory  lamp  associated  with  the  cord.  When  the 
local  subscriber  removes  his  receiver,  he  will  bridge  his  telephone  set 
across  the  line,  thereby  causing  the  battery  current  to  flow  through 
the  coil  of  relay  D.  The  energizing  of  relay  D  will  open  the  local  lamp 
circuit  and  extinguish  the  supervisory  signal,  thus  informing  the  toll 
operator  that  the  subscriber  has  answered. 

In  case  the  local  line  is  busy,  the  supervisory  lamp  associated  with 
the  toll  operator's  cord  will  not  light,  since  the  line  is  bridged  by  "the 
local  subscriber's  telephone.  In  this  case,  the  operator  may  either 
actuate  the  cut-off  key,  which  will  prevent  the  toll  subscriber  from 
listening  to  the  local  conversation,  and  wait  for  the  line  to  be  released; 
or,  if  the  toll  line  is  a  busy  one,  she  may  interrupt  the  local  conversa- 
tion and  tell  the  subscriber  that  a  long-distance  call  is  waiting,  with 
a  request  that  it  be  given  precedence. 

When  the  toll  conversation  has  been  completed  the  "  ring  off  " 
from  the  toll  line  will  actuate  the  clearing-out  drop  and  the  local 
subscriber  will  hang  up,  thus  de-energizing  relay  D  and  lighting  the 
supervisory  lamp.  The  toll  operator,  upon  seeing  the  disconnect 
signals,  will  take  down  the  cords,  which  in  turn  will  close  the  series 
contacts  in  the  trunk  jack  and  thus  energize  relay  A .  The  latter  will 
light  the  lamp  associated  with  the  trunk  at  the  local  board,  giving  the 
local  operator  a  disconnect  signal;  she  will  then  remove  the  connection 
and  so  restore  the  equipment  to  its  normal  state. 

In  case  the  toll  call  originates  at  the  local  exchange,  the  operator 
will  remove  the  answering  plug  and  insert  in  its  place  the  plug  of  a  two- 
way  toll  trunk.  This  will  light  the  lamp  associated  with  the  trunk 
at  the  toll  board,  due  to  the  operation  of  relays  A  and  B.  The  toll 
operator  will  then  answer  with  the  local  plug  of  a  pair  of  cords,  wrhich 
extinguishes  the  lamp,  and  thereafter  the  call  will  be  handled  in  the 
usual  manner.  If  the  desired  toll  line  is  busy,  or  if  it  requires  some 
time. to  complete  the  connection,  she  will  tell  the  subscriber  to  hang 
up  his  receiver  and  wait  until  called.  The  connection,  if  completed, 
will  be  handled  as  already  described. 

In  the  use  of  the  trunking  system  above  described,  it  must  be 


SMALL  TOLL  SWITCHBOARDS  69 

apparent  that  each  local  operator  should  have  at  least  one  two-way 
trunk  at  her  command.  A  very  desirable  distribution  of  this  type 
of  trunk  equipment  is  effected  by  placing  a  group  of  two  or  three 
trunks  between  each  pair  of  local  operators,  in  which  position  either 
operator  may  utilize  them.  It  will  be  readily  realized  from  this  that 
when  a  local  board  has  more  than  ten  equipped  positions,  the  number 
of  trunks  becomes  so  large  that  the  cost  of  installation  becomes  exces- 
sive; and  a  less  expensive  substitute  is  desirable.  This  difficulty 
may  be  obviated  by  placing  all  the  trunks  at  one  position.  In  this 
case  a  local  operator,  upon  receiving  a  toll  call,  will  instruct  the  opera- 
tor at  the  trunk  position  by  means  of  her  order  circuit,  as  to  the  number 
of  the  subscriber  who  desires  toll  service.  The  trunk  operator  will 
then  insert  one  of  the  trunk  plugs  in  the  multiple  jack  of  the  sub- 
scriber's line,  and  the  local  operator  at  whose  position  the  call  originated 
will  withdraw  the  answering  plug.  The  call  will  then  be  dealt  with 
in  the  manner  just  described. 

This  arrangement  of  the  trunking  equipment,  using  two-way  trunks, 
will  do  very  well  when  the  amount  of  toll  traffic  is  small,  but  when 
this  business  assumes  larger  proportions,  it  becomes  necessary  to 
adopt  different  methods.  Since  a  toll  call  must  go  through  the  hands 
of  two  operators  before  reaching  the  toll  board,  in  the  method  just 
described,  it  follows  that  this  will  give  rise  to  some  loss  of  time,  which 
can  be  avoided,  to  a  certain  extent,  by  a  system  that  employs  separate 
recording  and  incoming  toll  or  switching  trunks. 

Before  taking  up  the  detail  operation  of  this  system,  it  is  necessary 
to  have  a  clear  understanding  of  the  various  operations  required  in 
establishing  a  complete  connection.  In  order  to  appreciate  this  it 
becomes  essential  to  bear  in  mind  that  a  toll  exchange  is  a  means 
of  interconnecting  widely  separated  local  exchanges  by  long-distance 
toll  lines.  These  toll  lines,  as  already  stated  elsewhere,  are  in  reality 
trunks  connecting  various  towns  and  cities.  This  will  be  more  readily 
appreciated  by  referring  to  the  diagram  in  Fig.  35  which  is  divided 
into  four  parts  by  means  of  broken  lines  to  show  the  different  offices. 
The  sections  at  A  and  D  are  local  offices  and  those  at  B  and  C  are 
toll  offices. 

The  sequence  of  operations  in  a  call  is  briefly  as  follows:  When  a 
subscriber  at  exchange  A  desires  to  communicate  with  a  subscriber 
at  the  distant  exchange  D,  for  example,  the  local  operator  inserts  the 
calling  plug  in  an  idle  recording  trunk  jack  and  gives  the  connection 


TOLL  TELEPHONE  PRACTICE 


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SMALL  TOLL   SWITCHBOARDS  71 

no  further  attention  until  she  receives  the  disconnect  signal.  The 
recording  operator  at  office  B  then  answers  and  after  obtaining  the 
information  necessary  to  fill  out  a  toll  ticket,  informs  the  subscriber 
that  he  will  be  called  as  soon  as  the  connection  is  ready.  The  toll 
ticket  is  then  passed  to  the  toll-line  operator  at  the  B  office  who  has 
charge  of  the  desired  toll  line.  The  latter  operator  will  then  call  the 
toll-line  operator  at  the  C  office  in  the  usual  manner  and  ask  for  the 
particular  local  line  desired.  The  last-mentioned  operator  will  then 
communicate  to  the  trunk  operator  at  office  D,  by  means  of  an  order 
circuit,  the  number  of  the  local  subscriber  desired;  whereupon,  the 
trunk  operator  will  assign  the  trunk  and  complete  the  local  connection. 
The  toll  operator  at  C,  as  soon  as  she  gets  the  called  subscriber,  will 
signal  the  operator  at  B,  and  the  latter  will  then  call  the  subscriber 
at  A  who  originated  the  call;  the  connection  is  then  ready  for  conver- 
sation to  commence. 

It  is  evident  from  the  foregoing  that  a  toll  connection  can  only  be 
established  with  the  aid  of  several  operators.  The  call  passes  over 
the  various  circuits  in  the  order  indicated  by  the  numerals  of  the  dia- 
gram. This  method  of  handling  toll  connections  is  practically  stand- 
ard throughout  the  country  wherever  the  volume  of  business  does  not 
exceed  a  certain  limit. 

In  the  detailed  circuit  diagrams  which  follow,  showing  complete 
connections,  only  one  local  office  A  and  one  toll  office  B  will  be  shown; 
everything  to  the  right  of  the  dividing  line  E,  referring  to  Fig.  35, 
will  be  reduced  to  a  magneto  telephone  set.  This  is  done  to  make  the 
diagrams  as  simple  as  possible. 

Fig.  36  shows  one  of  the  forms  of  incoming  toll  (switching)  trunks 
which  has  been  used  considerably.  The  local  end  of  the  trunk  is 
usually  handled  by  the  operator  at  the  first  local  position,  as  the 
number  of  such  trunks  required,  in  connection  with  a  non-multiple 
toll  board  is  seldom  sufficient  to  keep  one  operator  busy.  The  opera- 
tion of  the  circuit  is  outlined  in  the  following  description,  it  being 
understood,  of  course,  that  this  circuit  merely  takes  the  place  of  the 
two-way  trunk  circuit  shown  in  Fig.  34.  Reference  will  be  made  to 
the  latter  in  connection  with  Fig.  36,  in  this  description.  The  toll 
operator,  in  handling  an  incoming  call,  will  answer  the  toll-line  signal 
in  the  usual  manner.  Upon  receiving  a  request  for  connection  with 
a  local  subscriber,  she  will  communicate  over  the  order  circuit  with 
the  operator  at  the  local  board  who  handles  the  toll  trunks,  giving  the 


72  TOLL  TELEPHONE  PRACTICE 

latter  the  number  of  the  subscriber  desired.  The  local  operator  will 
thereupon  assign  an  idle  trunk  and  connect  it  with  the  subscriber's 
line.  The  toll  operator  will  connect  with  her  end  of  the  trunk  by 
means  of  the  local  plug  of  the  cord  circuit  which  was  used  to  answer 
the  toll  line.  This  will  clear  the  trunk  circuit  of  all  signaling  appara- 
tus. If  the  local  line  is  not  in  use,  the  toll  operator  will  ring  the 
subscriber  in  the  usual  way.  When  the  conversation  has  been  com- 
pleted, the  toll  operator  will  receive  the  disconnect  signals  in  a  manner 


TOLL    BOARD 


LOCAL    BOARD 


llNCOMINQ    TQLU  TRUNK    CKT. 


FIG.  36.  —  Type  of  Incoming  Toll  Trunk  Used  with  a  Non-multiple  Toll  Board. 

similar  to  that  already  described  for  this  cord  circuit.  Upon  receiving 
these  signals  she  will  remove  the  cords,  thereby  closing  the  series 
contact  in  the  trunk  jack.  This  will  light  the  lamp  at  the  local  end 
of  the  trunk  over  the  circuit  traced  from  ground  by  way  of  relay  E  to 
the  sleeve  of  the  jack,  thence  over  the  ring  strand  of  the  trunk,  through 
the  jack  contact  and  relay  F  to  battery.  Relay  F  will  be  energized 
and  in  turn  will  light  the  disconnect  lamp.  The  local  operator,  upon 
receiving  this  disconnect  signal,  will  remove  the  trunk  cord,  which 
will  open  the  circuit  and  restore  all  equipment  to  its  normal  condition. 
Should  a  local  subscriber  call  for  a  toll  connection,  the  operator  will 
insert  the  calling  plug  of  the  cord  circuit  in  one  of  the  recording  trunk 
multiple  jacks,  after  she  has  made  the  usual  busy  test.  The  recording 
trunk  circuit  is  shown  in  Fig.  37.  A  circuit  will  be  completed  from 
battery  through  the  ring  relay  in  the  cord  circuit,  over  the  ring  con- 
ductor of  the  cord  and  the  trunk  through  relay  5,  the  back  contact  I 


SMALL  TOLL  SWITCHBOARDS 


73 


of  relay  A,  thence  through  the  contact  in  the  jack  and  back  to  battery 
(ground)  over  the  tip  strand  of  the  trunk  and  the  cord  and  the  tip 
relay.  Relay  A  is  not  operated  because  of  the  short-circuit  through 
the  jack  contacts.  At  the  same  time,  relay  B  lights  the  calling  lamp 
before  the  toll  recording  operator.  The  operation  of  both  relays  in 
the  cord  circuit  prevents  the  operation  of  the  supervisory  signal. 
When  the  recording  operator  answers,  the  short-circuit  in  relay  A  is 
removed  by  the  opening  of  the  jack  contacts;  thereupon  relay  A  re- 


TOLU  BOARD 


LOCAL  BOARD 


FIG.  37.  —  Type  of  Recording  Toll  Trunk  Used  with  a  Non-multiple  Toll  Board 

sponds  and  extinguishes  the  calling  signal.  After  taking  the  details 
of  the  call  from  the  subscriber,  the  operator  will  tell  him  to  hang  up 
his  receiver  and  wait  until  called.  Then  she  will  disconnect  from  the 
trunk.  This  will  establish  a  connection  to  ground  from  the  tip  strand 
of  the  trunk,  which  may  be  traced  from  the  jack  contact,  through  the 
contact  2  of  relay  A  and  thence  to  ground.  This  ground  connection 
serves  a  double  purpose;  first,  it  locks  relay  A,  which  was  already 
energized,  and  thus  prevents  the  relighting  of  the  calling  lamp;  and 
secondly,  it  shunts  the  tip  relay  in  the  local  cord  circuit,  which  in 
turn  releases,  and  lights  the  supervisory  lamp.  Thereupon  the  local 
operator  clears  the  connection  and  thus  restores  all  equipment  to  its 
normal  condition. 

The  ticket  which  bears  the  details  of  the  call  (toll  ticket)  is  then 
passed  to  the  toll-line  operator,  who  will  complete  the  connection  in 
accordance  with  the  procedure  before  outlined,  making  use  of  the  toll 
trunk  shown  in  Fig.  36. 


74 


TOLL  TELEPHONE  PRACTICE 


The  two-way  toll  trunk  as  shown  in  Fig.  34  and  the  incoming  toll 
trunk  shown  in  Fig.  36  have  no  provision  for  testing  the  multiple 
jacks  to  ascertain  whether  the  local  line  is  busy.  This  feature  can 
easily  be  added,  as  shown  in  Fig.  38,  by  placing  a  key  in  the  tip  con- 
ductor. This  key  in  its  normal  condition  closes  the  talking  circuit, 
but  upon  being  operated  opens  the  conductor  and  connects  the  plug 
end  of  the  cord  to  ground  through  the  induction  coil  in  the  operator's 


TOLL  SWITCHBOARP 


FIG.  38.  —  Two-way  Toll  Trunk  with  Busy-test  Key. 

set.  When  this  key  is  operated  and  the  tip  of  the  plug  is  applied  to 
the  sleeve  of  the  multiple  jack  of  the  busy  line,  the  flow  of  current  will 
give  the  operator  the  usual  busy  signal.  It  is  hardly  necessary  to 
add  that  the  operator,  when  provided  with  this  equipment,  should 
make  the  busy  test  before  assigning  the  trunk. 

It  is  hard  to  determine  whether  the  system  employing  the  key  for 
a  busy  test  is  an  advantage  or  not,  since  each  method  has  its  merits. 
The  chief  advantage  of  the  first  method  is  the  facility  with  which  a 
trunk  assignment  can  be  obtained,  regardless  of  whether  the  local 
line  is  busy.  It  also  saves  labor  at  the  local  board  and,  in  case  the 
local  line  subscriber  is  busy,  provides  a  busy  test  which  insures  pre- 
cedence for  the  toll  call  over  any  subsequent  calls.  One  of  the  principal 
advantages  of  the  second  method  is  the  freedom  from  interruption 
of  local  messages  by  the  toll  operators.  A  further  advantage  arises 
from  the  reduction  of  the  number  of  trunks  as  compared  with  the 
number  required  in  the  first  method,  due  to  a  smaller  average  holding 
time. 


CHAPTER  VII 
MULTIPLE-DROP   TOLL   SWITCHBOARDS 

WHEN  the  number  of  subscribers  in  a  non-multiple  local  switch- 
board becomes  so  large  that  three  or  four  operators  are  unable  to 
properly  handle  the  traffic,  it  is  common  practice  to  adopt  the  multiple 
type  of  board.  This  applies  also  to  toll  boards,  and  since  the  discussion 
of  the  non-multiple  toll  board  has  been  completed,  the  study  of  the 
multiple  type  is  now  in  order.  In  a  multiple  toll  board,  as  the  name 
implies,  all  the  toll  lines  entering  the  office  are  placed  in  front  of  each 
operator;  that  is,  the  lines  are  multipled  in  each  section  in  a  manner 
identical  with  that  used  in  the  local  multiple  switchboard.  Thus 
the  necessity  of  transferring  calls  is  obviated,  since  every  toll  operator 
is  able  to  call  any  toll  office  or  toll  subscriber  direct  from  the  multiple. 
Consequently  any  local-to-toll  connections  can  be  handled  by  any  toll 
operator,  since  all  the  toll  lines  in  the  office  can  readily  be  reached  in 
the  multiple;  whereas  in  a  non-multiple  board,  the  call  would  have  to 
be  given  to  the  operator  at  whose  position  the  desired  line  terminated. 
The  local-to-toll  business,  therefore,  can  be  more  evenly  distributed 
among  the  operators  in  a  multiple  board;  whereas  in  a  non-multiple 
board  this  is  not  possible.  From  the  foregoing  statements  it  is  evi- 
dent that  by  means  of  a  multiple  toll  board  it  is  possible  to  operate 
much  faster  and  therefore  more  efficiently.  These  items  become 
factors  worthy  of  consideration  when  the  toll  business  has  assumed 
large  proportions.  However,  a  multiple  toll  equipment  makes  the 
use  of  a  recording  operator  imperative.  This  operator,  as  previously 
explained,  does  all  the  clerical  work  for  local-to-toll  connections; 
that  is,  she  makes  out  all  toll  tickets  for  outgoing  calls.  It  will  be 
evident  that  this  division  of  labor  results  in  greater  accuracy  and  speed 
and  higher  efficiency  in  the  operators'  work. 

The  multiple  toll  boards  may  be  divided  into  three  distinctly 
separate  groups.  These  are,  first,  those  using  drop  signals  exclusively; 
second,  those  employing  only  lamp  signals;  and  third,  those  combining 
both  drop  and  lamp  signals.  Local  conditions  to  a  great  extent 

75 


76  TOLL  TELEPHONE  PRACTICE 

determine  the  kind  of  equipment  best  suited  to  any  particular  office. 
In  a  drop  board  the  panel  equipment  for  a  certain  number  of  lines 
requires  more  space  than  the  apparatus  necessary  for  the  same  number 
in  a  lamp  board.  However,  the  lamp  board  is  more  expensive  than 
the  drop  board.  The  principal  reason  for  this  is  that  all  the  equip- 
ment in  a  drop  board,  both  for  lines  and  cords,  can  readily  be  placed 
in  the  switchboard  framework,  thus  avoiding  the  installation  of  a 
relay  rack  in  the  terminal  room  and  the  necessary  cable  from  this 
rack  to  the  board.  But  it  is  often  an  advantage  to  have  the  line  equip- 
ment on  a  separate  rack,  where,  if  neatly  numbered,  it  is  readily 
found  by  the  repair  man  in  clearing  trouble.  In  a  lamp  board  it  is 
customary  to  distribute  the  equipment  in  this  manner.  It  is  under- 
stood, of  course,  that  in  a  lamp  equipment  a  line  relay  is  used  with 
each  toll  line,  in  place  of  the  drop  in  the  non-multiple  boards  previously 
described.  This  relay  has  two  windings,  one  of  which  is  connected 
directly  across  the  line  and  is  actuated  by  incoming  ringing  current, 
while  the  second  is  merely  a  locking  winding,  which  holds  the  arma- 
ture in  place  after  it  has  been  drawn  up  by  the  alternating  impulses. 
This  line  relay  and  the  associated  cut-off  relay  are  mounted  on  the 
rack  in  a  manner  similar  to  that  employed  for  the  same  relays  in  a 
local  common  battery  equipment.  One  of  the  objections  which  may 
be  raised  to  the  lamp  board  is  that  on  account  of  the  use  of  a  line  relay 
the  action  is  not  as  positive  as  it  is  in  the  drop  system,  because  there 
are  chances  for  trouble  in  the  local  circuit  from  the  relay  to  the  board, 
such  as  a  burnt-out  lamp  or  a  poor  relay  contact.  Therefore  an 
incoming  signal  might  fail  to  reach  the  board,  which  would  be  less 
likely  to  happen  with  the  other  type  of  equipment.  It  must  be 
obvious  that  the  circuits  in  a  lamp  board  are  more  complex  than  those 
used  in  a  drop  board,  and  for  this  reason  the  drop  board  is  preferable 
where  skilled  attendance  is  not  available.  One  of  the  very  desirable 
features  of  a  lamp  board  is  the  facility  for  mounting  the  line  signal 
immediately  above  the  jack,  which  is  not  advisable  in  a  drop  board 
for  reasons  explained  in  Chapter  VI. 

All  toll  lines  should  be  cabled  from  the  high-current  arresters  to 
the  main  distributing  frame  and  thence  to  the  intermediate  frame; 
from  the  latter  they  should  be  carried  directly  to  the  answering  jacks. 
The  use  of  a  connecting  rack  at  the  rear  of  the  board,  as  a  substitute 
for  the  intermediate  frame,  is  not  good  practice.  The  objection  to 
the  use  of  a  rack  is  the  lack  of  flexibility.  In  laying  out  the  cable 


MULTIPLE-DROP  TOLL  SWITCHBOARDS  77 

runs  in  a  toll  board  installation  all  sharp  corners  should  be  avoided, 
since  it  is  the  general  experience  that  these  are  weak  spots  of  an  instal- 
lation; when  a  high  potential  current  finds  its  way  into  the  board,  such 
sharp  turns  are  frequently  the  seat  of  burn-outs.  A  sharp  corner  may 
appear  more  sightly,  but  this  is  an  instance  where  appearance  should 
be  sacrificed  to  insure  reliability  and  freedom  from  trouble. 

Before  going  into  a  detailed  description  of  either  type  of  board,  the 
methods  of  obtaining  the  busy  test  on  multiple  toll  boards  will  be 
considered  briefly.  There  are  two  standard  methods  of  obtaining 
this  test:  first,  the  well-known  audible  test,  and  second,  a  visual  test, 
employing  a  signal  associated  with  each  multiple  jack.  The  audible 
test  is  applicable  to  either  system,  while  the  visual  test  is  not  desirable 
in  a  drop  board,  but  may  be  used  with  excellent  results  in  a  lamp 
board.  The  use  of  visual  busy  signals  is  not  entirely  successful  in 
drop  boards  because  a  short  interval  of  time  elapses  during  which  a 
line  may  be  busy  while  the  signal  does  not  indicate  that  condition. 
This  is  due  to  the  fact  that  the  busy  signal  is  energized  by  the  operation 
of  the  cut-off  relay  and  therefore  there  is  no  indication  that  the  line 
is  busy  from  the  time  the  drop  falls  until  the  toll-line  operator  answers. 
While  this  interval  may  be  but  a  few  seconds  at  the  most,  it  is  long 
enough  to  permit  another  operator  to  take  up  the  line  in  the  multiple. 
In  a  lamp  board  the  conditions  are  different,  because  the  local  circuit 
through  the  busy  signal  is  closed  by  a  contact  on  the  line  relay;  and 
when  the  cut-off  relay  is  energized  (releasing  the  line  relay)  it  again 
closes  a  battery  circuit  through  the  signals,  so  that  they  indicate  a 
"  busy  line  "  from  the  time  an  incoming  ring  is  received  until  the 
operator  takes  down  the  connection.  These  conditions  will  be  de- 
scribed in  detail  after  each  system  has  been  discussed,  and  the  opera- 
tions may  then  be  comprehended  more  readily. 

Since  a  drop  board  is  the  simplest  form  of  multiple  toll  equipment, 
a  detailed  analysis  of  this  type  will  be  considered  first  and  will  occupy 
the  remainder  of  this  chapter.  The  best  means  of  obtaining  a  clear 
conception  of  an  equipment  of  this  kind  is  to  study  each  class  of 
connection  separately;  that  is,  toll-to-toll,  toll-to-local  and  local-to- 
toll,  under  various  conditions,  as  indicated  by  the  headings  which 
hereafter  appear. 


78  TOLL  TELEPHONE  PRACTICE 

Joint  Toll  and  Local  Offices:  Two-wire  Local  Board 

(a)  Toll-to-Toll  Connection.  —  A  connection  of  this  character  is 
independent,  of  course,  of  the  local  office  and  will  be  disposed  of  first. 
The  complete  circuit  appears  in  Fig.  39.  By  referring  to  this  drawing 
it  will  be  observed  that  the  toll-line  drop  is  bridged  across  the  line 
through  the  break  contacts  of  relay  A.  The  function  of  this  relay 
is  identical  with  that  of  the  cut-off  relay  in  a  subscriber's  line  circuit; 
that  is,  it  disconnects  the  drop  from  the  toll  line.  This  improves  the 
efficiency  of  both  signaling  and  transmission.  The  cord  circuit  is  a 
through  metallic  connection,  the  tip  conductor  of  which  is  normally 
open  to  provide  suitable  means  for  obtaining  the  busy  test. 

The  operation  of  the  circuit  is  as  follows:  An  incoming  toll-line 
signal  will  actuate  the  drop  in  the  usual  manner.  The  operator  upon 
seeing  the  signal  will  plug  into  the  answering  jack  and  thus  complete 
a  circuit  from  battery  through  the  winding  of  relay  A,  which  will 
open  the  line  contacts  to  the  drop.  The  act  of  plugging  in  will  also 
raise  the  potential  of  the  sleeve  strand  of  the  jack  and  hence  should 
an  operator  test  any  multiple  jack  of  this  line,  she  will  obtain  the  busy 
signal.  The  operator  will  then  bridge  her  telephone  set  across  the 
line  by  operating  key  4,  and  ascertain  the  details  of  the  call;  if  the 
line  called  for  is  idle  she  will  plug  in  and  ring.  Due  to  the  insertion 
of  the  plug,  the  potential  of  the  sleeve  strand  of  the  line  jack  will  be 
raised  as  before,  and  at  the  same  time  a  circuit  will  be  established  from 
the  ground  on  relay  At  over  the  sleeve  conductor,  through  relay  B  to 
battery,  which  will  operate  relays  A  and  B.  The  operation  of  relay  A 
disconnects  the  drop  from  the  line,  while  that  of  relay  B  opens  the 
test  circuit  and  at  the  same  time  closes  the  tip  strand  of  the  cord, 
which  completes  the  circuit  between  the  two  toll  lines.  When  the 
conversation  is  completed  the  ring-off  signal  will  actuate  the  clearing- 
out  drop,  which  is  permanently  bridged  across  the  cord  circuit;  and 
the  operator  upon  receiving  this  signal  will  take  down  the  connections. 
In  case  the  desired  line  is  busy,  however,  the  sleeve  strand  of  the  jack 
associated  with  this  line  will  have  had  its  potential  raised  by  virtue 
of  the  plug  previously  inserted;  and  the  operator,  upon  testing  the 
multiple,  will  receive  the  usual  busy  signal.  This  circuit  may  be  traced 
from  the  negative  side  of  battery  to  the  sleeve  of  the  jack  and  by  way 
of  the  tip  strand  of  the  cord,  through  the  break  contact  of  relay  B  and 
the  tertiary  winding  of  the  induction  coil,  to  ground.  The  operator, 


MULTIPLE-DROP  TOLL  SWITCHBOARDS 


79 


8o  TOLL  TELEPHONE  PRACTICE 

upon  learning  that  the  line  is  busy,  will  so  inform  the  calling  operator 
or  subscriber.  It  will  be  observed  that  this  circuit  is  provided  with 
a  double  cut-off  key  2  and  3,  so  that  the  operator  can  converse  over 
either  line,  individually,  if  she  so  desires. 

(b)  Toll-to-Local  Connection.  —  In  a  toll-to-toll  connection  the 
operator  is  in  a  position  to  complete  the  entire  connection  without 
further  assistance,  but  when  she  desires  a  local  subscriber  she  must 
call  the  trunk  operator,  who  is  situated  at  the  local  board,  for  a  trunk 
assignment.  The  trunk  circuit  to  the  local  board,  together  with  a 
complete  diagram  of  a  toll-to-local  connection,  is  shown  in  Fig. -40. 
As  would  be  naturally  inferred,  and  as  the  circuit  shows,  the  toll  end 
of  the  connection  remains  the  same,  while  the  cord  circuit  is  no  longer 
a  through  metallic  connection,  but  is  divided  into  two  distinct  parts; 
one  end  is  adapted  to  the  toll  line  and  the  other  to  the  local  trunk, 
these  two  parts  being  connected  inductively  by  means  of  the  repeat- 
ing coil.  The  trunk  circuit  is  plug-ended  at  the  local  board,  and  all 
trunks  terminate  at  the  trunk  operator's  position;  while  at  the  toll 
board  the  trunk  is  jack-ended  and  these  jacks  are  multipled  in  each 
toll  section  so  as  to  be  readily  accessible  to  each  operator. 

The  operation  of  the  circuit  is  as  follows:  The  toll  operator  will, 
by  means  of  her  order  circuit,  place  herself  in  communication  with  the 
trunk  operator  and  inform  her  as  to  the  number  of  the  local  subscriber 
desired.  The  trunk  operator  upon  receiving  this  information  will 
operate  key  6  (non-locking)  associated  with  one  of  the  idle  trunks 
and  proceed  to  test  the  jack  of  the  line  called  for.  If  the  line  is  idle 
she  will  plug  into  the  jack,  at  the  same  time  giving  the  toll  operator 
the  trunk  assignment.  When  the  trunk  operator  inserts  the  plug  a 
circuit  can  be  traced  from  the  ground  at  relay  Z),  over  the  ring  con- 
ductor of  the  cord,  through  the  series  contacts  in  the  trunk  jack  and 
via  relay  E  to  battery.  Due  to  the  completion  of  this  circuit,  relays 
D  and  E  will  be  energized;  the  operation  of  D  disconnects  the  signaling 
apparatus  from  the  line,  while  E  closes  the  local  lamp  circuit  and  thus 
lights  the  trunk  supervisory  lamp  at  the  local  board.  However,  this 
lamp  will  remain  lighted  but  a  short  interval,  since  the  toll  operator, 
upon  receiving  the  trunk  assignment,  will  plug  into  the  trunk  jack;  this 
will  open  the  jack  contacts  and  break  the  circuit  just  established,  thus 
releasing  relay  E.  Relay  D  will  remain  energized,  since  a  circuit  can 
be  traced  from  the  ground  at  D,  over  the  sleeve  strand  of  the  line, 
thence  over  the  ring  conductors  of  the  trunk  and  cord  circuits  and 


MULTIPLE-DROP  TOLL  SWITCHBOARDS 


8l 


fVVWYWV > 

Em*k 


82 


TOLL  TELEPHONE  PRACTICE 


through  relay  H  to  battery.  This  will  energize  relay  H  and  thus 
light  the  toll  supervisory  lamp.  The  lighting  of  this  lamp  will  show 
the  toll  operator  that  the  local  end  of  the  connection  has  been  com- 
pleted, while  the  extinguishment  of  the  trunk  lamp  will  inform  the 
trunk  operator  that  the  toll  end  has  been  taken  up.  The  toll  operator 
is  now  ready  to  ring  the  subscriber,  which  she  does  in  the  regular 
manner.  When  the  subscriber  answers  he  bridges  his  telephone  set 
across  the  line,  which  causes  current  to  flow  over  the  toll  cord  circuit 
through  relays  H  and  G.  This  will  operate  relay  G  and  extinguish 
the  toll  supervisory  lamp,  thereby  informing  the  operator  that  the 
subscriber  has  answered.  When  the  conversation  is  completed  the 
clearing-out  signal  from  the  toll  line  will  actuate  the  clearing-out  drop. 
The  local  subscriber  will  hang  up  his  receiver  and  thus  release  relay  G. 
This  will  light  the  toll  supervisory  lamp  and  thus  give  the  toll  operator 
the  disconnect  signal.  The  latter  will  then  take  down  the  connection. 
The  removal  of  the  plug  from  the  trunk  jack  will  open  the  circuit 
through  relay  H  and  thus  extinguish  the  supervisory  lamp ;  it  will  also 
close  the  series  contacts  in  the  trunk  jack.  Thus  the  circuit  through 
relay  E,  as  explained  above,  will  be  reestablished,  and,  consequently, 
this  will  light  the  trunk  supervisory  lamp,  giving  the  trunk  operator 


FlG.  41.  —  Combination  Cord  Circuit  for  a  Multiple-drop  Toll  Board. 

a  disconnect  signal.  She  will  then  take  down  the  cord  and  thus 
restore  the  apparatus  to  its  normal  condition.  In  case  the  toll  opera- 
tor orders  up  a  local  line  which  is  busy,  the  trunk  operator  will  so 
inform  her,  and  this  information  will  be  passed  back  over  the  toll  line. 
Thus  far  in  the  description  of  the  multiple -drop  toll  board  the  cord 
circuits  shown  have  been  adaptable  to  one  class  of  service  only.  A 


MULTIPLE-DROP  TOLL   SWITCHBOARDS  83 

circuit  embodying  the  essential  features  of  the  last  two  cord  circuits 
described,  and  far  superior  to  either,  is  the  combination  toll-to-toll  and 
toll-to-local  circuit  shown  in  Fig.  41.  This  circuit  in  its  normal 
condition  is  arranged  for  toll-to-local  connections,  as  shown  in  the 
sketch,  the  two  lines  being  connected  inductively  by  means  of  the 
repeating  coil;  battery  current  is  fed  to  the  local  subscriber's  station 
through  the  coils  of  relays  A  and  B.  The  only  operation  necessary 
to  convert  the  circuit  into  a  through  metallic  cord,  for  toll-to-toll 
service,  is  the  operation  of  key  5,  which  cuts  out  the  repeating  coil 
and  the  local  supervisory  apparatus.  The  advantages  of  a  circuit 
of  this  type  have  been  fully  discussed  in  Chapter  VI;  and,  as  the 
operation  of  the  circuit  is  identical  with  the  two  last  described,  further 
discussion  is  unnecessary. 

(c)  Local-to-Toll  Connections.  —  The  local-to-toll  connections  nat- 
urally bring  to  mind  the  recording  toll  operator  and  her  functions. 
The  recording  circuits,  together  with  those  necessary  to  complete  a 
local-to-toll  connection,  are  illustrated  in  Fig.  42.  It  will  be  observed 
that  the  recording  trunk  terminates  in  jacks  at  both  ends,  the  local- 
board  end  being  multipled  in  each  section  of  the  board  so  as  to  be 
accessible  to  all  operators.  At  the  toll  board  the  trunks  all  terminate 
in  jacks  before  the  recording  operators. 

The  method  of  handling  a  local-to-toll  connection  is  as  follows: 
A  local  operator,  having  been  asked  for  toll,  will  test  the  recording 
trunk  jacks  until  she  finds  one  which  is  idle.  She  will  then  connect 
the  subscriber  with  the  trunk.  The  act  of  plugging  into  a  recording 
trunk  jack  will  raise  the  potential  of  the  sleeve  of  the  jack  and  thus 
put  a  busy  test  on  the  multiple.  At  the  same  time  a  circuit  will  be 
established  from  battery,  through  the  coil  F  of  the  calling  supervisory 
relay,  over  the  ring  strand  of  the  cord  and  thence  by  way  of  the  sleeve 
strand  of  the  trunk,  through  relay  H  to  ground.  Relay  H  will  thus 
be  energized  and  will  close  a  circuit  from  the  ground  on  the  make 
contact  of  relay  H  to  the  break  contact  of  relay  G,  through  the  lamps 
associated  with  the  trunk  used  and  thence  to  battery.  Consequently 
these  lamps  will  be  lighted  and  will  attract  the  attention  of  a  recording 
operator.  The  calling  supervisory  lamp  in  the  local  cord  circuit  will 
also  be  lighted,  due  to  the  energizing  of  coil  F  of  the  calling  supervisory 
relay.  The  recording  operator,  upon  plugging  into  the  trunk  jack, 
completes  a  circuit  from  battery  through  coil  L  and  thence  over  the 
sleeve  strand  of  the  cord  and  trunk,  through  relay  K  and  thus  to 


84 


TOLL  TELEPHONE  PRACTICE 


MULTIPLE-DROP  TOLL  SWITCHBOARDS  85 

ground.  This  will  cause  the  operation  of  relay  K  and  in  turn  will 
complete  the  two  following  circuits.  First,  the  attraction  of  armature 
i  of  the  relay  will  bridge  the  retardation  coil  /  across  the  recording 
trunk,  which  in  turn  will  cause  current  to  pass  through  coil  E  of  the 
calling  supervisory  relay  in  the  local  cord  circuit.  Since  the  magnetic 
pull  of  coil  E  opposes  that  of  coil  F,  the  retractile  spring  will  have 
sufficient  strength  to  draw  up  the  armature  and  extinguish  the 
local  supervisory  lamp;  this  will  inform  the  local  operator  that  the 
recording  operator  has  answered  the  call.  Second,  the  attraction  of 
the  other  armature  of  relay  K  will  close  a  circuit  from  battery  through 
the  make  contact,  thence  through  relay  G  and  to  ground  through  the 
make  contact  of  relay  H.  Consequently  the  armatures  of  relay  G 
will  be  drawn  up,  and  will  be  locked  by  the  make  contact  on  armature 
i,  by  means  of  the  circuit  that  may  be  traced  from  battery  through 
the  make  contact,  the  armature,  the  coil  of  relay  G,  and  thence  to 
ground  through  the  make  contact  of  relay  H.  Relay  G  will  not  be 
unlocked  until  relay  H  is  de -energized.  The  attraction  of  armature  2 
will  break  the  lamp  circuit,  thereby  extinguishing  the  recording  trunk 
lamps.  The  recording  operator  will  then  take  the  details  of  the  call 
from  the  subscriber  and  make  out  a  toll  ticket.  She  will  then  tell 
the  subscriber  to  hang  up  his  receiver  and  advise  him  that  he  will  be 
called  when  the  connection  is  ready.  She  will  then  disconnect  from 
the  trunk,  thus  releasing  relay  K.  This  will  open  the  circuit  of  the 
bridged  retardation  coil  /,  which  in  turn  will  de-energize  coil  E  of 
the  supervisory  relay  and  thus  light  the  lamp  in  the  local  cord.  The 
recording  lamp  will  not  relight,  owing  to  the  fact  that  relay  G  is 
still  energized  by  means  of  the  locking  scheme  previously  described. 
When  the  local  subscriber  hangs  up  his  receiver,  the  answering  super- 
visory lamp  in  the  local  cord  will  also  light  and  the  local  operator,  upon 
seeing  these  signals,  will  remove  the  connections.  The  withdrawal 
of  the  plug  from  the  recording  jack  will  release  relay  H,  which  in  turn 
will  unlock  relay  G  and  thus  restore  the  apparatus  to  its  normal 
condition.  The  recording  operator  will  then  pass  the  toll  ticket  to 
the  proper  toll-line  operator,  who  will  obtain  the  subscriber  desired 
and  complete  the  connection  as  though  it  were  a  toll-to-local  call. 


86  TOLL  TELEPHONE  PRACTICE 

Separate  Toll  and  Local  Office:  Two-wire  Local  Board 

(a)  Toll-to-Local  Connection.  —  The  trunking  circuits  just  de- 
scribed in  Figs.  40  and  42  should  be  used  only  when  the  toll  and  local 
boards  are  in  the  same  building.  This  follows  from  the  design  of 
the  circuits,  which  require  three  wires  in  each  trunk  between  the 
boards.  Such  a  condition  is  met  when  there  is  but  one  local  office 
in  a  city  or  town.  If  there  are  two  or  more  local  offices  a  two-wire 
trunking  system  is  necessary  for  reasons  of  economy.  Under  the 
latter  circumstances  it  is  sometimes  best  to  locate  the  toll  office  near 
the  city  outskirts,  at  or  adjacent  to  a  junction  of  the  toll  lines,  in  order 
to  minimize  the  wire  mileage  in  through  connections.  This  is  not 
universal  practice,  however,  even  though  it  is  often  the  best  method 
from  a  theoretical  standpoint.  Another  method  places  the  toll  office 
in  the  same  building  with  the  largest  local  office.  This  is  the  practice 
followed  by  the  Kinloch  Telephone  Company  of  St.  Louis,  and  a 
description  of  their  method  of  handling  traffic  between  the  toll  board 
and  the  local  branch  offices  will  be  given  next. 

A  theoretical  diagram  of  the  circuit  used  for  the  toll- to-local  con- 
nections in  this  system  is  shown  in  Fig.  43.  It  will  be  observed  that 
the  toll  cord  circuit  is  equipped  with  lamp  supervision;  the  toll-line 
signals  are  drops,  however,  and  therefore  this  board  comes  under  the 
classification  of  "Combined  Drop  and  Lamp  Boards,"  referred  to  pre- 
viously. The  cord  circuit  is  universal  and  somewhat  special  in  design; 
a  single  lamp  gives  the  disconnect  signal  for  toll-to-toll  connections, 
but  a  double  disconnect  signal  is  obtained  on  toll-to-local  connections. 
This  will  be  very  evident  from  an  inspection,  so  no  further  description 
of  the  operation  of  the  cord  circuit  will  be  given,  except  as  it  affects 
the  operation  of  an  incoming  toll  trunk. 

The  toll  board  end  of  the  trunk  circuit  terminates  in  a  spring  jack 
as  shown;  these  jacks  are  multipled  in  each  section  of  the  toll  board. 
At  the  local  board  the  trunk  is  plug-ended,  these  plugs  being  situated 
at  the  toll  trunk  positions  in  the  various  branch  offices.  The  method 
of  handling  a  toll-to-local  call,  including  the  operation  of  the  above 
circuit,  is  as  follows:  The  toll  operator  will  communicate,  by  means 
of  an  order  circuit,  with  the  trunk  operator  at  the  particular  local 
office  in  which  the  desired  subscriber's  line  terminates,  asking  for  a 
trunk  assignment.  The  trunk  operator  will  then  test  the  multiple 
jack  of  the  line  called  for;  if  the  line  is  idle,  she  will  plug  in  and  ring, 


MULTIPLE-DROP  TOLL  SWITCHBOARDS 


88  TOLL  TELEPHONE  PRACTICE 

at  the  same  time  giving  the  toll  operator  the  trunk  assignment.  Here- 
in lies  the  chief  disadvantage  of  this  system,  since  the  work  of  ringing 
the  local  subscriber  is  transferred  to  the  trunk  operator.  It  will  be 
remembered  that  in  the  circuit  shown  in  Fig.  40  the  ringing  was 
attended  to  by  the  toll  operator,  and  thereby  gave  her  complete  control 
of  the  connection;  whereas  in  this  system  the  toll  operator  must 
depend  upon  the  trunk  operator  for  this  part  of  the  work.  When  the 
trunk  operator  inserts  the  plug  just  referred  to,  a  circuit  may  be 
traced  from  the  ground  on  the  line  cut-off  relay  (not  shown)  to  the 
sleeve  of  the  multiple  jack  and  thence  over  the  ring  strand  of  the  trunk 
plug  and  cord,  through  relay  J  to  battery.  Therefore,  relay  /  will 
be  energized;  armature  i  will  open  the  lead  to  the  operator's  telephone 
set  and  at  the  same  time  close  the  tip  strand  of  the  talking  circuit. 
The  attraction  of  armature  2  will  close  a  circuit  through  the  disconnect 
and  the  ringing  lamps,  which  will  consequently  be  lighted.  The  cir- 
cuit through  the  disconnect  lamp  can  be  traced  from  the  ground  on 
armature  2  of  relay  /  to  the  break  contact  and  armature  of  relay  K 
and  thence  through  the  lamp  to  battery;  the  circuit  containing  the 
ringing  lamp  may  be  followed  from  the  ground  on  the  armature  of 
relay  J  to  the  armature  and  break  contact  of  relay  M  and  thence 
through  the  lamp  to  battery.  In  the  meantime,  however,  the  toll 
operator  will  have  inserted  a  plug  in  the  multiple  trunk  jack  assigned, 
thereby  causing  a  flow  of  current  from  the  ground  on  the  retardation 
coil  N  to  the  sleeve  strand  of  the  trunk  jacks  and  the  cord  circuit 
through  relay  F  to  battery.  This  will  cause  the  operation  of  relay  F, 
which  will  remove  the  test  connection  from  the  tip  of  the  cord  and 
close  the  tip  strand  of  the  cord  circuit.  The  insertion  of  the  plug  of 
the  toll  cord  will  also  close  a  circuit  which  can  be  traced  from  the  ground 
on  armature  2  of  relay  L,  by  way  of  the  break  contact  to  winding  3 
of  the  repeating  coil,  thence  to  the  ring  strands  of  the  trunk  and  the 
toll  cord  circuits,  through  the  bridged  relay  E,  returning  over  the  tip 
strands  of  the  cord  and  the  trunk  circuits,  through  winding  i  of  the 
repeating  coil,  to  the  break  contact  and  armature  i  of  relay  L  and 
thence  through  relay  K  to  battery.  The  completion  of  this  circuit 
will  cause  the  operation  of  relays  E  and  K.  The  operation  of  relay  E 
will  light  the  supervisory  lamp  in  the  toll  cord  circuit,  thereby  inform- 
ing the  operator  that  the  subscriber  has  not  answered.  The  operation 
of  relay  K  will  extinguish  the  disconnect  lamp  at  the  local  end  of  the 
trunk,  by  opening  its  circuit.  The  trunk  operator  then  knows  that 


MULTIPLE-DROP  TOLL  SWITCHBOARDS  89 

the  connection  at  the  toll  board  has  been  taken  up.  When  the  local 
subscriber  answers,  a  circuit  will  be  completed  from  the  ground  on  the 
coil  of  relay  L  to  the  tip  strand  of  the  trunk  and  thence  by  way 
of  the  subscriber's  line  circuit,  to  the  ring  of  the  trunk  and  through 
relay  /  to  battery.  This  will  operate  relay  L,  and  the  attraction  of 
its  armatures  will  open  the  circuit  through  relay  E  in  the  toll  cord 
circuit,  by  means  of  the  break  contacts.  This  will  extinguish  the  lamp 
in  the  cord  circuit.  Furthermore,  the  attraction  of  armature  i  of 
relay  L  will  maintain  the  circuit  through  relay  K,  by  means  of  the 
ground  on  the  make  contact.  The  attraction  of  armature  2  of  relay  L 
will  close  a  circuit  from  ground  to  the  make  contact  and  the  coil  of 
relay  M  to  battery.  Thus  relay  M  will  open  the  circuit  containing 
the  ringing  lamp  and  close  a  circuit  that  can  be  traced  from  the  ground 
on  armature  2  of  relay  /,  through  the  armature,  make  contact  and 
winding  of  relay  M,  to  battery.  The  latter  will  lock  relay  M  until 
the  subsequent  release  of  relay  /.  The  ringing  lamp  in  the  trunk 
circuit  and  the  supervisory  lamp  in  the  toll  cord  circuit  have  now  been 
extinguished,  thus  informing  both  operators  that  the  local  subscriber 
has  answered.  The  toll  connection  can  now  be  completed  if  the 
calling  subscriber  is  waiting  on  the  line.  The  toll  operator  will  then 
supervise  the  connection  until  conversation  starts  satisfactorily. 

When  the  subscribers  have  finished  talking,  the  distant  toll  operator 
will  ring  off,  thereby  energizing  relay  D  which  will  lock  itself  and  thus 
light  the  answering  supervisory  lamp  in  the  toll  cord  circuit.  The 
action  of  relay  D  will  be  explained  more  fully  under  the  description 
of  the  multiple-lamp  toll  board  in  a  subsequent  chapter.  The  local 
subscriber,  by  hanging  up  his  receiver,  will  open  his  line  circuit  and 
consequently  relay  L  will  be  de-energized.  This  will  again  close  the 
circuit  through  relay  E  and  thus  light  the  calling  supervisory  lamp 
in  the  toll  cord  circuit.  The  release  of  relay  L  will  have  no  effect  upon 
the  trunk  operator's  signals,  as  relay  M  will  remain  energized  until 
relay  /  is  released;  therefore,  the  ringing  lamp  circuit  remains  open. 
When  the  toll  operator  receives  the  disconnect  signals,  she  will  operate 
her  listening  key  to  make  certain  that  the  subscribers  are  through 
talking;  she  will  then  operate  the  calculagraph  and  take  down  the 
connections.  This  will  open  the  circuit  containing  relay  K  and  its 
subsequent  release  will  close  the  circuit  containing  the  disconnect 
lamp.  The  lighting  of  the  lamp  will  give  the  trunk  operator  a  dis- 
connect signal  and  she  will  thereupon  take  down  the  connection. 


9° 


TOLL  TELEPHONE  PRACTICE 


This  will  release  relay  J  which,  in  turn,  will  release  relay  M  and  thus 
restore  the  apparatus  to  its  normal  condition. 

(b)  Local-to-Toll  Connection.  —  There  now  remains  but  one  class 
of  service  that  has  not  been  explained  in  connection  with  this  type  of 
equipment,  namely,  the  local-to-toll  connection.  In  Fig.  44  is  shown 
the  recording  trunk  circuit  used  for  this  purpose.  This  trunk  will 
operate  with  the  circuits  shown  in  the  toll-to-local  connection  in  Fig.42, 
replacing  the  trunk  circuit  shown  in  that  figure.  The  recording  trunk 
shown  in  Fig.  44  is  the  one  used  in  the  St.  Louis  toll  board  in  con- 


FIG.  44.  —  Two-wire  Recording  Trunk  Circuit,  Kinlock  Telephone  Company,  St.  Louis. 

junction  with  the  branch  offices.  These  branch  offices  are  equipped 
with  the  Kellogg  Switchboard  and  Supply  Company's  four-relay  cord 
circuit;  but  as  the  operation  of  this  circuit  is  identical,  theoreti- 
cally, with  the  Stromberg-Carlson  cord  circuit  shown  in  Fig.  42,  it  is 
possible  to  refer  to  the  latter  in  the  following  description  of  the  opera- 
tion of  the  trunk  shown  in  Fig.  44. 

In  the  use  of  this  circuit  the  local  operator,  upon  being  informed  by 
the  calling  subscriber  that  a  toll  connection  is  desired,  will  test  the 
recording  multiple  until  an  idle  trunk  is  found  and  then  complete  the 
connection.  This  will  complete  a  circuit  from  battery  through  coil 
F  of  the  supervisory  relay  in  the  local  cord  circuit  to  the  ground 
attached  to  coil  G  on  the  ring  strand  of  the  recording  jack,  thus  oper- 
ating the  relay  and  lighting  the  supervisory  lamp;  this  will  also  raise 
the  potential  on  the  sleeve  of  the  jack,  thus  placing  a  busy  test  on  the 
trunk  multiple.  At  the  same  time  a  circuit  will  be  established  which 
may  be  traced  as  follows:  from  battery  through  coil  F  of  the  super- 


MULTIPLE-DROP  TOLL  SWITCHBOARDS  91 

visory  relay  in  the  cord  circuit,  over  the  ring  strand  of  the  cord  and 
the  trunk,  through  relay  H  and  thence  by  way  of  the  tip  strand  of 
the  trunk  and  the  cord  through  coil  E  of  the  supervisory  relay  in  the 
cord  circuit,  to  ground.  Due  to  the  very  high  resistance  of  relay  H, 
the  local  supervisory  relay  will  not  operate,  while  the  large  number  of 
turns  on  relay  H  will  cause  it  to  respond  and  close  a  circuit  that  may 
be  traced  as  follows :  from  ground  on  the  armature  of  relay  H,  by  way 
of  the  make  contact,  to  the  armature  and  the  break  contact  of  relay  /, 
and  thence  through  the  recording  lamp  to  battery.  This  lamp  will 
light  and  signal  the  operator  to  answer.  The  act  of  plugging  into  the 
jack  will  complete  a  circuit  from  the  battery  through  coil  L,  by  way 
of  the  sleeve  strands  of  the  recording  cord  and  trunk  circuits,  through 
relay  /  to  ground.  This  will  operate  relay  /  and  the  subsequent 
attractions  of  armature  i  will  place  the  2oo-ohm  relay  K  in  parallel 
with  the  i5,ooo-ohm  relay  H,  thereby  decreasing  the  current  in  the 
latter  sufficiently  to  permit  it  to  release.  Furthermore,  the  closing  of 
the  circuit  through  relay  K  will  allow  enough  current  to  flow  through 
coil  E  of  the  supervisory  relay  in  the  local  cord  circuit  to  cause  its  oper- 
ation, thereby  extinguishing  the  local  supervisory  lamp  and  informing 
the  local  operator  that  the  call  has  been  answered.  Since  the  circuit 
through  relay  K  has  been  closed,  it  will  be  actuated  and  will  complete 
the  following  circuit :  from  the  ground  on  the  make  contact  of  relay  K, 
by  way  of  the  armature,  through  the  coil  of  relay  /,  to  the  make  con- 
tact and  armature  2  of  relay  /,  to  battery.  Relay  /  will  thus  be 
energized  and  the  subsequent  attraction  of  armature  2  will  extinguish 
the  recording  lamp,  while  the  attraction  of  armature  i  will  lock  the 
relay  by  means  of  a  circuit  which  can  be  traced  from  the  battery  on 
the  make  contact,  by  way  of  armature  i  and  the  coil  of  the  relay,  to 
the  armature  and  make  contact  of  relay  K,  to  ground.  Relay  7  will 
therefore  remain  closed  until  relay  K  is  de-energized.  The  recording 
operator  is  now  ready  to  converse  with  the  subscriber.  Having 
obtained  the  necessary  information  she  will  request  him  to  hang  up 
his  receiver.  The  act  of  hanging  up  the  receiver  will  light  the  answer- 
ing supervisory  lamp  in  the  local  cord  circuit,  while  the  removal  of  the 
recording  plug  will  open  the  circuit  containing  relay  /;  this  in  turn  will 
remove  the  shunt  around  relay  H  and  cause  it  to  respond.  The  coil 
E  of  the  supervisory  relay  in  the  local  cord  will  be  in  circuit  again  with 
the  high-wound  relay  and  the  current  will  be  insufficient  to  hold  up 
its  armature,  which  will  light  the  calling  supervisory  lamp  in  the  local 


Q2  TOLL  TELEPHONE  PRACTICE 

cord.  The  recording  lamp  will  not  relight,  because  relay  /  is  still 
energized.  The  latter  condition  results  as  follows.  When  the  record- 
ing operator  removes  the  plug,  as  explained  above,  the  armature  of 
relay  K  falls  back  and  relay  H  is  immediately  energized,  thus  shifting 
the  ground  connection  from  the  make  contact  of  relay  K  to  the  make 
contact  of  relay  H\  and  since  relay  K  is  designed  to  be  slow  acting, 
this  shift  is  made  before  the  make  contact  of  relay  K  is  broken,  and 
hence  relay  /  remains  locked.  This  locking  circuit  can  be  traced  from 
the  ground  on  the  armature  of  relay  H,  by  way  of  the  make  contact, 
through  the  coil  of  relay  /,  the  armature  and  the  make  contact  of  the 
latter,  to  battery.  Now,  as  stated  above,  the  supervisory  lamps  in 
the  local  cord  circuit  have  been  lighted  and  consequently  the  local 
operator  will  remove  the  connections.  This  will  open  the  circuit 
through  relay  H,  which  in  turn  will  release  relay  /  and  thus  restore 
the  apparatus  to  its  normal  condition. 

The  discussion  of  the  multiple -drop  toll  board  has  been  confined 
thus  far  to  the  equipment,  which  is  necessary  for  operation  in  con- 
junction with  a  two-wire  local  equipment,  strictly  speaking.  The 
other  type  of  toll  equipment  is  the  one  which  operates  in  connection 
with  the  three -wire  local  board.  An  example  of  the  second  type  is 
the  equipment  which  has  been  used  by 'the  American  Telephone  and 
Telegraph  Company,  illustrated  in  Fig.  45.  The  design  of  these  cir- 
cuits is  such  that  they  should  be  used  -only  where  the  toll  and  local 
boards  are  in  the  same  building,  because  three  wires  are  used  in  the 
inter-board  trunks.  Inasmuch  as  "a  toll-to-toll  connection  with  the 
equipment  about  to  be  described  is  practically  identical  with  that 
outlined  in  connection  with  Fig.  39,  no  further  comment  on  that  type 
of  connection  will  be  necessary.  The  description  will  be  confined, 
therefore,  to  the  trunking  equipment. 

Joint  Toll  and  Local  Offices:  Three-wire  Local  Board 

(a)  Local- to-Toll  Connection. — The  operation  of  the  circuit  shown 
in  Fig.  45  is  as  follows.  When  a  local  operator  ascertains  that  a  toll 
connection  is  desired,  she  communicates  with  the  incoming  trunk 
operator  by  means  of  an  order  circuit,  giving  the  latter  the  number  of 
the  local  subscriber  desiring  the  toll  connection.  The  trunk  operator 
will  thereupon  insert  the  plug  of  one  of  the  toll  trunks  in  the  multiple 
jack  associated  with  the  subscriber's  line.  She  disregards  the  busy 
test  on  this  jack,  which  she  receives  because  of  the  plug  that  was 


MULTIPLE-DROP  TOLL  SWITCHBOARDS 


93 


*  * 

If 

•§  a 
1| 
!•§. 


3g 

2  -o 


94  TOLL  TELEPHONE  PRACTICE 

previously  inserted  in  the  answering  jack  by  the  local  operator.  The 
local  operator  will  then  withdraw  the  answering  plug.  The  insertion 
of  the  trunk  plug  in  the  multiple  jack  of  the  local  line  will  actuate 
relay  A,  the  operation  of  which  will  remove  the  busy  test  connection 
from  the  tip  of  the  plug  and  close  the  tip  talking  strand.  This  will 
also  connect  the  ground,  attached  to  armature  2,  to  one  side  of  the 
disconnect  lamp.  This  lamp  will  not  be  lighted,  however,  since  the 
circuit  to  battery  is  open  at  the  make  contact  of  relay  B.  The  in- 
sertion of  the  trunk  plug  and  the  subsequent  operation  of  relay  A  will 
close  a  circuit  through  the  double -wound  relay  E.  This  circuit  may 
be  traced  from  ground  by  way  of  armature  i  and  the  make  contact 
of  relay  C,  through  one  of  the  8o-ohm  windings  of  relay  E,  to  the  tip 
strand  of  the  trunk  and  thence  to  the  line;  then,  since  the  subscriber's 
receiver  is  off  the  hook,  the  circuit  is  completed  by  way  of  the  ring 
strand  of  the  line  and  trunk,  through  the  other  8o-ohm  winding  of 
relay  E,  to  the  break  contact  and  armature  2  of  relay  C,  to  battery. 
Relay  E  is  thus  energized  and  will  light  the  white  lamp  at  the  recording 
operator's  position.  This  lamp  circuit  can  be  followed  from  the  ground 
on  the  armature  of  relay  E,  over  the  make  contact,  to  armature  2  of 
relay  D  and  then  via  the  break  contact  through  the  lamp  and  pilot 
relay  to  battery.  It  will  be  noted  that  the  white  lamp  is  shunted  by 
means  of  a  3oo-ohm  resistance  coil.  The  resistance  of  this  coil  is  so 
great  that  the  major  part  of  the  current  will  flow  through  the  lamp; 
but  should  the  lamp  burn  out,  this  resistance  will  provide  a  path  by 
means  of  which  the  pilot  relay  will  be  energized.  The  pilot  lamp  in 
that  case  will  light,  thus  notifying  the  recording  operator  that  a  call 
is  waiting  and  she  will  proceed  to  operate  her  listening  keys  until  she 
finds  the  particular  trunk.  Upon  seeing  the  white  lamp  displayed, 
the  recording  operator  will  operate  the  listening  key  associated  with 
this  trunk,  and  obtain  from  the  subscriber  the  details  of  his  call. 
The  operation  of  the  listening  key,  in  addition  to  bridging  the  recording 
operator's  telephone  set  across  the  trunk,  will  close  the  make  contact 
on  this  key.  The  closing  of  this  contact  completes  a  circuit  which 
may  be  traced  from  ground  through  the  winding  of  relay  D,  to  the 
make  contact  in  the  key  and  then  by  way  of  the  2io-ohm  resistance 
coil  to  battery.  This  will  energize  relay  D  and  the  attraction  of  its 
armatures  will  perform  several  functions.  First,  the  attraction  of 
armature  i  will  lock  the  relay  by  means  of  a  circuit  from  ground 
through  the  winding  to  armature  i  and  thence  by  way  of  the  make 


MULTIPLE-DROP  TOLL  SWITCHBOARDS  95 

contact  and  the  2io-ohm  resistance  coil  to  battery;  second,  the  attrac- 
tion of  armature  2  will  substitute  a  green  lamp  for  the  white  lamp 
previously  mentioned.  The  object  of  furnishing  these  two  lamps  is 
to  prevent  a  second  answer  by  the  recording  operator  while  the  toll 
ticket  is  on  its  way  to  the  line  operator.  It  is  necessary  that  the 
recording  operator  be  provided  with  some  signal  which  will  inform  her 
that  the  line  operator  has  taken  up  the  trunk.  This  could  be  accom- 
plished by  re -lighting  the  white  lamp  but  it  might  lead  to  the  complica- 
tion just  mentioned. 

When  the  recording  operator  has  completed  the  toll  ticket,  she  will 
pass  it  to  the  regular  line  operator  who  is  to  complete  the  connection. 
When  the  latter  receives  the  ticket,  she  will  insert  the  plug  of  the  local 
end  of  one  of  her  regular  cord  circuits  in  the  designated  trunk  jack, 
which  will  actuate  relay  C  due  to  the  fact  that  battery  is  connected 
to  the  sleeve  of  the  toll  plug  and  ground  is  connected  to  the  sleeve  of 
the  trunk  jack  by  way  of  the  coil  winding  of  relay  C.  The  operation 
of  relay  C  will  de -energize  relay  E,  since  the  circuit  by  means  of  which 
the  latter  was  energized,  is  opened  at  armatures  i  and  2  of  relay  C. 
This  \vill  extinguish  the  green  lamp  at  the  recording  operator's  position 
because  the  lamp  circuit  is  opened  at  the  armature  of  relay  E.  The 
recording  operator  knows,  therefore,  that  the  toll  operator  has  taken 
up  the  connection.  The  attraction  of  armature  i  of  relay  C  also 
unlocks  relay  D,  as  the  winding  of  D  is  now  shunted  by  a  path  from 
armature  i  of  this  relay  to  the  make  contact  of  armature  i  on  relay  C 
and  then  to  ground.  The  unlocking  of  relay  D  restores  all  the  ap- 
paratus to  normal,  except  relay  C  at  the  recording  position,  which 
remains  energized  as  long  as  the  plug  of  the  toll  cord  remains  in  the 
trunk  jack;  relay  C  thereby  prevents  the  further  operation  of  any  of 
the  recording  equipment.  The  operation  of  relay  C  closes  another 
circuit  which  can  be  traced  from  battery  to  armature  2  of  the  relay 
and  then  by  way  of  the  make  contact,  through  the  4o-ohm  winding  of 
relay  B,  through  the  loo-ohm  resistance  coil  and  the  make  contact  of 
relay  A,  through  the  armature  and  thus  to  ground.  Thus  relay  B 
will  be  energized  and  locked,  due  to  the  circuit  that  can  be  traced  from 
battery  to  the  armature  of  relay  B  and  thence  by  way  of  the  make 
contact,  the  2o-ohm  winding,  the  disconnect  lamp,  the  loo-ohm  resist- 
ance coil  and  the  make  contact  and  armature  2  of  relay  At  to  ground. 
This  locking  circuit  will  remain  effective  and  hold  up  the  armature 
of  relay  B  until  the  connection  is  finally  broken  by  the  withdrawal  of 


96  TOLL  TELEPHONE  PRACTICE 

the  trunk  plug  from  the  multiple  jack.  The  disconnect  lamp  con- 
tained in  the  last  circuit  will  not  be  lighted  because  it  is  shunted  by  the 
4o-ohm  winding  of  relay  B.  The  toll  operator,  having  plugged  into 
the  trunk  jack  with  the  local  plug  of  a  pair  of  cords,  will  next  insert 
the  toll  plug  in  the  jack  of  the  toll  line  and  proceed  to  pass  the  call. 
When  the  called  subscriber  is  ready,  the  conversation  can  be  started 
and  the  toll  operator  will  stamp  the  ticket  in  the  calculagraph  to  time 
the  connection.  When  the  conversation  is  completed  the  local  sub- 
scriber will  hang  up  his  receiver  and  thus  light  the  supervisory  lamp 
in  the  toll  cord  circuit  in  the  regular  manner.  The  toll  operator  will 
thereupon  operate  the  listening  key  in  the  cord  circuit  to  determine 
whether  the  conversation  is  finished.  The  operation  of  the  listening 
key  will  restore  the  clearing-out  drop  in  case  it  has  been  actuated, 
since  a  circuit  is  established  through  the  restoring  winding  of  this 
drop  by  means  of  the  make  contacts  on  the  listening  key.  If  the 
toll  operator,  upon  listening-in,  learns  that  no  further  service  is 
desired,  she  will  take  down  the  connections.  The  removal  of  the 
local  plug  from  the  trunk  jack  will  open  the  circuit  containing  relay 
C.  This  relay  will  thus  be  released.  The  restoring  of  armature  2 
will  open  the  shunt  circuit  around  the  disconnect  lamp;  the  latter, 
therefore,  will  light  and  give  the  local  trunk  operator  a  disconnect 
signal.  She  will  then  take  down  the  trunk  connection  and  restore  the 
apparatus  to  normal. 

(b)  Toll-to-Local  Connection.  —  A  distant  toll  operator  calling  the 
office  in  the  usual  manner  will  be  answered  by  the  line  operator,  who 
uses  the  toll  end  of  one  of  the  cord  circuits.  The  line  drop  will  be 
automatically  restored  at  the  same  time,  by  the  actuation  of  the  re- 
storing coil.  The  line  operator,  upon  ascertaining  that  a  local  con- 
nection is  desired,  will  make  out  a  ticket  and  order  up  a  trunk  at  the 
local  trunking  position,  by  means  of  her  order  circuit.  The  trunk 
operator  will  thereupon  test  the  jack  of  the  local  line  desired  and,  if 
it  is  idle,  will  insert  the  toll  trunk  plug,  at  the  same  time  giving  the 
line  operator  the  trunk  assignment.  The  latter  will  then  insert  the 
plug  of  the  local  end  of  the  cord  circuit  in  the  jack  of  the  trunk  assigned, 
which  will  energize  relay  C.  The  insertion  of  the  trunk  plug  at  the 
trunking  position  will  energize  relay  A ;  and  since  relay  C  is  already 
energized,  the  circuit  through  the  4o-ohm  winding  of  relay  B  will  be 
closed,  and  this  relay  will  lock  itself  as  explained  in  the  local-to-toll 
connection.  The  disconnect  lamp  at  the  switching  position  will  not 


MULTIPLE-DROP  TOLL   SWITCHBOARDS 


97 


98  TOLL  TELEPHONE  PRACTICE 

light,  however,  due  to  the  fact  that  the  shunt  circuit  around  this  lamp 
is  closed  at  the  make  contact  on  armature  2  of  relay  C.  The  operation 
of  relay  C  is  the  only  one  which  takes  place  in  the  apparatus  at  the 
recording  position,  since  this  relay  is  operated  before  the  subscriber 
answers,  and  hence  the  circuit  through  the  two  windings  of  relay  E 
is  permanently  opened.  Thus  the  recording  operator  will  not  be  dis- 
turbed by  any  false  signals.  Now,  as  the  local  subscriber's  receiver  is 
on  the  hook,  the  supervisory  lamp  in  the  toll  cord  circuit  will  light  and 
remain  in  this  condition  until  the  subscriber  answers.  The  toll  operator 
is  then  in  a  position  to  ring  the  subscriber.  When  he  answers,  the 
supervisory  lamp  in  the  toll  cord  will  be  extinguished  and  then  the 
line  operator  will  see  that  conversation  starts.  Upon  the  completion 
of  the  conversation,  the  disconnect  signals  will  be  obtained  in  the 
manner  previously  described. 

There  now  remains  to  be  shown  the  design  of  the  circuits  used  by 
the  American  Telephone  and  Telegraph  Company  when  the  local  and 
the  toll  offices  are  in  separate  buildings.  The  design  of  the  trunk 
circuit  there  used  is  a  radical  departure  from  anything  thus  far  shown, 
since  the  repeating  coil,  which  heretofore  has  been  situated  in  the  cord 
circuit,  is  transferred  to  the  trunk  circuit.  This  serves  to  establish 
an  objectionable  feature  in  the  respect  that  the  trunk  operator  must 
ring  the  local  subscriber,  as  it  is  impractical  to  ring  through  the  re- 
peating coil.  Thus  the  toll  operator  loses  complete  control  of  the 
connection. 

Separate  Toll  and  Local  Offices:  Three-wire  Local  Board 

(a)  Local-to-Toll  Connection.  —  The  circuits  employed  with  this 
type  of  equipment  are  shown  in  Fig.  47.  The  subscriber,  after  signal- 
ing the  local  operator  in  the  usual  manner,  will  be  trunked  to  the 
recording  operator  in  the  manner  previously  described,  when  the 
offices  are  in  the  same  building.  The  incoming  trunk  operator  will 
insert  the  plug  of  an  idle  trunk  in  the  subscriber's  multiple,  disregard- 
ing the  busy  test;  the  local  operator  will  then  disconnect  from  the 
answering  jack.  The  insertion  of  the  plug  by  the  trunk  operator 
will  close  a  circuit  from  ground  through  the  winding  of  the  cut-off 
relay,  thence  over  the  sleeve  of  the  jack  and  the  sleeve  strand  of  the 
cord,  through  the  winding  of  relay  A  and  the  ringing  lamp  to  battery. 
Thus  relay  A  will  be  energized  and  the  attraction  of  armature  i  will 
disconnect  the  testing  circuit  from  the  tip  of  the  plug  and  at  the  same 


100  TOLL  TELEPHONE  PRACTICE 

time  close  the  tip  talking  strand.  The  ringing  lamp,  in  the  closed 
circuit  just  outlined,  will  not  light  on  account  of  the  actuation  of 
relay  F,  which  in  turn  energizes  relay  B  and  shunts  the  lamp  by  means 
of  the  4o-ohm  locking  winding.  Relay  F  is  energized  because  the 
subscriber's  receiver  is  off  the  hook;  and  hence  the  battery  will  find 
a  path  from  ground  by  way  of  winding  i  of  the  repeating  coil,  to  the 
tip  of  the  trunk  and  line  through  the  subscriber's  set,  returning  by  way 
of  the  ring  strand  of  the  line  and  trunk,  through  relay  F  to  winding  3 
of  the  repeating  coil  and  battery.  The  operation  of  relay  F  will  close 
a  circuit  from  the  ground  on  the  armature,  to  the  make  contact  and 
through  the  windings  of  relays  B  and  E  to  battery.  Relay  B  is  thus 
energized  through  the  6o-ohm  winding  and  will  lock  through  the  4o-ohm 
winding.  The  actuation  of  relay  E  and  the  subsequent  attraction  of 
armature  i  has  no  immediate  effect  upon  the  apparatus.  The  attrac- 
tion of  armature  2,  however,  opens  a  circuit  which  normally  is  closed 
through  relay  /.  This  circuit  is  traceable  from  ground,  through  the 
winding  of  the  relay,  to  armature  2  of  relay  H\  and  thence  by  way  of 
the  break  contact  of  the  latter,  through  the  ring  strand  of  the  trunk 
and  winding  4  of  the  repeating  coil,  to  armature  2,  and  the  break 
contact  of  relay  E,  to  battery.  Relay  /  is  thus  de-energized  and  will 
close  a  circuit  from  the  ground  on  its  armature  to  armature  2  and  the 
break  contact  of  relay  G,  through  the  white  recording  lamp  and  then  to 
battery.  The  lamp  is  therefore  lighted  and  the  recording  operator,  upon 
seeing  this  signal  displayed,  will  actuate  the  listening  key  associated 
with  the  trunk.  This  will  bridge  her  telephone  set  across  the  circuit  so 
that  she  can  converse  with  the  subscriber.  Due  to  the  extra  set  of  make- 
contact  springs  on  the  recording  operator's  listening  key,  a  circuit  is 
closed  from  the  ground  at  these  springs  through  relay  G  to  battery. 
Thus  relay  G  will  be  energized  and  attract  its  armatures.  The  at- 
traction of  armature  i  locks  this  relay,  owing  to  the  establishment  of  a 
circuit  that  can  be  traced  from  the  ground  on  armature  i  of  relay  H, 
by  way  of  the  break  contact  of  armature  i  of  relay  G,  and  the  make 
contact  and  coil  of  this  relay  to  battery.  This  relay  is  actuated,  there- 
fore, as  long  as  relay  H  remains  energized.  The  attraction  of  arma- 
ture 2  of  relay  G  opens  the  circuit  containing  the  white  recording 
lamp  previously  mentioned,  and  closes  a  similar  circuit  containing  a 
green  lamp.  The  restoration  of  the  listening  key,  however,  does  not 
extinguish  the  green  lamp)  because  of  the  locking  circuit  just  referred 
to.  The  purpose  of  these  two  signals  is  to  give  positive  super- 


MULTIPLE-DROP  TOLL  SWITCHBOARDS  101 

vision  as  indicated  in  the  description  of  the  system  immediately 
preceding. 

The  operation  has  now  been  traced  to  the  toll-line  operator.  This 
operator,  upon  receiving  the  toll  ticket,  will  insert  the  answering  plug 
of  one  of  the  toll  cords  in  the  multiple  jack  of  the  trunk  designated. 
This  will  close  a  circuit  from  the  battery  connection  on  the  sleeve  of 
the  toll  cord,  to  the  sleeve  of  the  trunk  jack  and  through  the  coil  of 
relay  H  to  ground.  The  attraction  of  armature  i  of  relay  H  opens 
the  locking  circuit  through  the  coil  of  relay  G;  the  latter  will  be 
released,  thus  opening  the  circuit  Containing  the  green  recording  lamp. 
The  extinguishment  of  this  lamp  informs  the  recording  operator  that 
the  line  operator  has  taken  up  the  connection.  The  attraction  of 
armature  2  of  relay  H  will  close  a  circuit  from  the  ground  at  the  coil 
of  relay  /,  to  armature  2  of  relay  H  and  then  to  battery.  Relay  /  is 
thus  energized  and  prevents  the  relighting  of  the  white  recording  lamp. 
The  apparatus  at  the  recording  position,  with  the  exception  of  relay  H, 
is  now  in  its  normal  condition,  and  will  remain  so  until  the  toll  plug 
is  withdrawn  from  the  trunk  jack,  which  will  release  relay  H.  The 
line  operator  will  now  proceed,  to  complete  the  connection  as  previously 
described.  When  the  conversation  is  completed,  the  clearing-out 
drop  in  the  toll  cord  circuit  will  be  actuated  either  by  a  clearing-out 
signal  from  the  toll  line  or  by  the  subscriber's  act  of  hanging  up  his 
receiver.  The  operation  of  the  former  circuit  is  self-evident;  but  the 
latter  is  somewhat  difficult  and  therefore  will  be  explained. 

When  the  local  subscriber  hangs  up  his  receiver,  the  line  circuit  is 
opened  at  his  instrument,  which  causes  the  release  of  relay  F  and  in 
turn  the  release  of  relay  E.  The  return  to  normal  of  the  armatures 
of  relay  E  closes  a  circuit  from  the  ground  on  armature  i  and  the 
break  contact  of  this  relay,  to  the  winding  of  relay  D  and  the  winding 
2  of  the  repeating  coil,  over  the  tip  side  of  the  trunk  and  cord  circuits, 
thence  through  the  winding  of  the  clearing-out  drop  and  over  the  ring 
side  of  the  cord  and  trunk,  through  the  winding  4  of  the  repeating  coil, 
and  armature  2  and  the  break  contact  of  relay  E  to  battery.  The 
completion  of  this  circuit  will  actuate  the  drop  and  also  energize 
relay  D ;  the  latter,  in  turn,  will  close  a  circuit  from  the  ground  on  its 
armature  to  the  make  contact,  thence  through  the  4o-ohm  resistance 
coil,  the  winding  of  relay  C,  the  make  contact  and  armature  2  of  relay 
A  and  then  to  battery.  Relay  C  will  then  close  a  circuit  from  ground, 
through  the  disconnect  lamp,  to  the  armature  and  make  contact  of 


102  TOLL  TELEPHONE  PRACTICE 

relay  C,  the  coil  of  the  latter,  and  the  make  contact  and  armature  2 
of  relay  A,  to  battery.  Relay  C  is  'locked,  therefore,  through  the 
make  contact  and  armature  2  of  relay  A  and  will  remain  so  until  the 
trunk  operator  takes  down  the  connection.  The  disconnect  lamp 
contained  in  this  locking  circuit  will  not  light,  however,  due  to  the 
shunt  circuit  established  by  the  4O-ohm  resistance  coil  and  the  arma- 
ture of  relay  D,  to  ground.  However,  when  the  toll  operator  obtains 
the  clearing-out  signal,  she  will  take  down  the  connections  and  this 
will  open  the  circuit  containing  the  coil  of  relay  Z>,  previously  traced. 
The  release  of  relay  D  will  open  "the  shunt  around  the  disconnect 
lamp.  The  lighting  of  this  lamp  will  give  the  trunk  operator  the 
disconnect  signal  and  she  will  take  down  the  trunk  connection,  which 
will  release  relay  A  and  consequently  relay  C.  All  apparatus  will 
then  be  restored  to  its  normal  condition. 

(b)  Toll-to-Local  Connection.  —  The  toll -line  operator,  upon  receipt 
of  an  inward  call,  will  communicate  with  the  trunk  operator  by  means 
of  the  order  circuit,  and  inform  her  as  to  the  number  of  the  local 
subscriber  desired.  The  trunk  operator  will  assign  a  trunk  and  test 
the  multiple  jack  of  the  local  line.  In  case  the  line  is  busy,  she  will 
insert  the  trunk  plug  in  a  busy-back  jack  to  give  the  toll  operator  a 
busy  signal.  If  the  line  is  idle,  she  will  insert  the  trunk  plug,  of 
course,  in  the  multiple  jack.  This  will  light  the  ringing  lamp  asso- 
ciated with  the  trunk  circuit,  due  to  the  fact  that  relay  F  is  not  ener- 
gized. The  trunk  operator  will  then  ring  the  local  subscriber.  When 
he  answers,  relay  F  will  be  energized  and  the  ringing  lamp  will  be 
extinguished,  as  explained  in  the  local-to-toll  connection.  In  the 
meantime,  the  toll  operator  will  have  inserted  the  calling  plug  of 
the  pair  of  cords  used  to  answer  the  incoming  toll  call  in  the  multiple 
jack  of  the  trunk  assigned.  This  will  have  operated  relay  H,  and 
thus  prevented  the  operation  of  the  remaining  apparatus  at  the 
recording  operator's  position.  The  subscriber  is  then  in  communi- 
cation with  the  line  operator,  and  the  connection  is  handled  in  the 
same  manner  as  described  for  the  local-to-toll  connection. 

It  will  be  observed  that  the  toll  cord  circuit  is  equipped  with  a 
key  K,  by  means  of  which  the  operator  may  disconnect  the  clearing- 
out  drop  from  the  circuit.  This  key  is  used  on  line  connections  only, 
when  it  becomes  necessary  to  improve  transmission  to  the  utmost;  in 
this  case,  the  removal  of  the  bridged  drop  will  slightly  improve  the 
talking  efficiency  of  the  circuit. 


MULTIPLE-DROP  TOLL   SWITCHBOARDS 


103 


Auxiliary  Toll  Board  Circuits.  —  A  discussion  of  some  of  the  local 
circuits  or  trunks,  used  in  connection  with  a  multiple-drop  toll  board, 
is  necessary  to  make  clear  the  methods  of  handling  any  calls  which 
involve  irregular  operations.  These  circuits  can  be  adapted,  with  few 
changes,  to  any  of  the  systems  previously  described  in  this  chapter. 

One  of  the  important  circuits  in  a  board  of  this  kind  is  the  inter- 
position trunk,  used  by  the  operators  for  intercommunication  and 


ANSWERING  POSITION 


FIG.  48.  —  Interposition  Trunk  Circuit. 

transfers.  At  first  sight  it  might  seem  that  a  circuit  of  this  kind 
would  be  detrimental  rather  than  beneficial,  owing  to  the  possibility 
that  operators  might  use  it  improperly  for  personal  conversation. 
However,  in  a  well-disciplined  office  cases  of  this  kind  should  be  rare. 
These  circuits  may  be  used  also  for  information  trunks;  in  this  case 
one  end  of  the  circuit  terminates  at  the  information  operator's  position. 
One  of  the  types  of  interposition  trunk  is  shown  in  Fig.  48.  It  will  be 
noted  that  the  circuit  is  jack-ended ;  these  jacks  are  multipled  in  each 
section  of  the  board,  so  as  to  be  accessible  to  all  line  operators.  It 
is  customary  to  place  a  designation  strip  directly  above  the  jacks,  by 


104  TOLL  TELEPHONE  PRACTICE 

means  of  which  they  may  be  suitably  numbered.  The  answering 
jacks  shown  at  the  "  answering  position  "  in  Fig.  48  (with  associated 
apparatus)  are  distributed  among  the  various  sections  or  positions, 
so  as  to  provide  universal  intercommunication.  The  lamp  shown  is 
usually  placed  in  the  pilot  rail  so  as  to  make  it  as  conspicuous  as 
possible. 

The  operation  of  the  circuit  is  as  follows:  When  one  operator 
desires  to  communicate  with  another,  she  will  insert  the  local  plug  of 
one  of  her  cords  in  the  jack  of  the  trunk  which  terminates  before  the 
desired  operator.  This  operation  will  connect  battery  to  the  sleeve 
of  the  jack,  for  a  busy  test,  and  will  also  close  the  make  contact  in  the 
jack.  The  closing  of  this  contact  will  complete  a  circuit  which  can  be 
traced  from  the  ground  on  the  jack  contact,  along  wire  i  to  armature  i 
of  relay  A,  and  thence  through  the  interposition  lamp  to  battery. 
This  signal  will  order  the  desired  operator  to  answer;  the  latter  will 
do  so  with  the  local  plug  of  one  of  her  cord  circuits.  This  will  close 
the  jack  contact  in  the  answering  jack  and  thus  establish  a  circuit  from 
battery  through  the  coil  of  relay  A  (and  the  contact  just  mentioned), 
thence  over  wire  i,  through  the  make  contact  in  the  calling  operator's 
jack  and  then  to  ground.  The  operation  of  relay  A,  by  means  of 
armature  i,  will  open  the  circuit  containing  the  interposition  trunk 
lamp  and  extinguish  the  latter.  The  attraction  of  armature  2  will 
close  a  circuit  from  the  make  contact  and  armature  2  on  relay  A, 
through  the  coil  of  relay  B  to  wire  i.  It  will  be  observed  that  relay 
B  is  short-circuited  by  part  of  the  circuit  previously  traced,  that  is, 
by  the  wire  from  armature  2  of  relay  A ,  to  wire  i  of  the  trunk.  There- 
fore relay  B  will  not  operate. 

The  operators  are  now  directly  connected  by  means  of  wires  2 
and  3.  When  the  called  operator  disconnects,  the  short-circuit  on  relay 
B  will  be  removed.  This  relay  will  then  operate  and  connect  battery 
to  the  ring  side  and  ground  to  the  tip  side  of  the  line,  which  will  cause 
the  operation  of  the  supervisory  relay  in  the  cord  circuit  at  the  calling 
operator's  position  and  give  her  a  disconnect  signal.  This  operator 
will  then  remove  the  connection,  which  will  release  relay  B  and  restore 
the  apparatus  to  normal. 

Another  auxiliary  circuit  which  helps  to  reduce  the  labor  of  opera- 
tion considerably  is  the  shifting  receiving  circuit  sometimes  used  at 
the  recording  positions,  and  shown  in  Fig.  49.  This  diagram  shows 
two  recording  operator's  positions  and  a  multiple  of  three  trunks;  the 


MULTIPLE-DROP  TOLL   SWITCHBOARDS 


105 


106  TOLL  TELEPHONE  PRACTICE 

general  scheme  can  be  extended  to  cover  any  number  of  positions. 
The  primary  purpose  of  this  circuit  is  to  switch  an  incoming  call  to 
the  first  idle  position.  Furthermore,  each  position  is  so  arranged 
that  it  can  be  taken  out  of  service  and  the  calls  which  would  be 
received  switched  automatically  to  the  next  position  in  service. 
This  is  of  special  advantage  during  the  periods  of  light  traffic,  when 
only  one  or  possibly  two  operators  are  necessary  to  handle  the  work; 
in  this  case,  these  operators  can  be  grouped  in  any  manner  desired. 
This  will  become  evident  after  the  operation  has  been  described.  It 
will  be  noted  that  each  recording  lamp  is  wired  through  the  pilot 
relay  to  battery.  Hence  an  incoming  call  will  light  the  recording 
trunk  lamp  and  energize  the  pilot  relay.  Consequently,  if  key  i  is 
in  its  normal  position,  a  circuit  can  be  traced  from  the  ground  on  the 
armature  of  the  pilot  relay,  by  way  of  the  make  contact,  to  the  make 
contact  in  key  i,  and  thence  through  the  pilot  lamp  to  battery,  thus 
lighting  the  pilot  lamp.  It  may  be  well  to  state  that  although  the 
circuit  shows  three  cord  circuits  per  position,  the  operator  has  use 
for  but  one;  and  the  other  two  are  installed  only  as  a  reserve  in  case 
of  trouble.  The  keys  of  these  reserve  cord  circuits  are  always  kept  in 
the  listening  position  so  as  to  permit  the  transfer  of  calls  to  the  next 
position,  as  will  be  explained  later  on.  Furthermore,  a  recording 
operator  answers  only  when  both  the  line  and  the  pilot  lamps  light, 
the  latter  being  the  operator's  individual  signal. 

An  incoming  call  has  been  traced  to  the  lighting  of  the  pilot  lamp 
in  position  i;  the  operator  at  this  position,  upon  seeing  the  lighted 
pilot  lamp,  will  plug  into  the  jack  associated  with  the  lighted  trunk 
lamp,  operate  key  i  and  answer  the  call.  The  act  of  plugging  into  the 
trunk  jack  will  extinguish  the  trunk  lamp  and  likewise  the  pilot  lamp, 
as  previously  described.  The  operation  of  the  key  will  open  the  break 
contact  and  close  the  make  contact;  and  since  keys  2  and  3  are  also 
in  the  listening  position,  as  before  stated,  their  contacts  will  be  in  a 
similar  condition.  Assuming  that  while  the  first  operator  is  answer- 
ing a  call,  a  second  call  comes  in,  the  operation  will  be  as  follows: 
The  trunk  lamps  will  light  at  each  position  and  energize  the  pilot 
relay;  but  the  pilot  lamp  circuit  at  the  first  position  is  open  at  the 
keys  and  consequently  the  second  pilot  will  light  because  a  new  cir- 
cuit has  been  established  from  the  contacts  of  the  pilot  relay,  through 
the  keys  at  the  first  position.  This  circuit  can  be  traced  from 
the  ground  on  the  armature  of  the  pilot  relay,  by  way  of  the  make 


MULTIPLE-DROP  TOLL  SWITCHBOARDS  107 

contact  of  this  relay  and  the  make  contacts  of  keys  i,  2  and  3  at 
position  i,  to  the  break  contact  of  key  i  at  position  2,  and  thence 
through  the  pilot  lamp  at  position  2  to  battery.  The  operator  at 
position  2,  upon  seeing  the  lighted  pilot  lamp,  will  insert  a  plug  in  the 
jack  associated  with  the  lighted  trunk  lamp,  thereby  extinguishing  the 
latter  and  the  pilot.  This  operator  will  also  have  the  keys  of  the  two 
cords  not  in  use  in  the  listening  position ;  hence  the  next  incoming  call 
will  be  transferred  to  the  third  or  next  idle  operator  in  a  manner 
identical  with  that  just  described.  When  all  the  keys  in  all  the 
positions  are  thrown,  the  circuit  through  the  buzzer  will  be  closed, 
thus  giving  the  overflow  alarm ;  this  will  notify  the  supervisor  that  the 
number  of  operators  at  the  recording  position  is  inadequate  to  handle 
the  traffic.  It  is  understood,  of  course,  that  the  bridging  of  the  re- 
cording operator's  set  across  the  trunk  will  give  the  operator  at  a 
two- wire  local  board  the  usual  cord  supervision. 

The  circuits  used  in  connection  with  the  multiple-drop  toll  board 
have  now  been  fully  discussed;  it  remains  to  describe  how  the  apparatus 
used  with  these  circuits  is  distributed  through  the  switchboard  sections 
so  as  to  give  the  best  economy  from  an  operating  standpoint.  Having 
this  in  view,  there  is  shown  in  Fig.  50  a  fully  equipped  toll-line  ter- 
minal section,  designed  for  ah  ultimate  capacity  of  sixty  toll  lines. 
The  usual  method  of  distributing  the  apparatus  is  practically  uniform 
for  all  sections;  hence  the  description  will  be  confined  to  a  single 
section.  It  will  be  noted  that  all  the  drops  have  been  placed  above 
the  other  equipment,  so  as  to  occupy  the  most  conspicuous  position; 
furthermore,  their  operation  is  not  as  likely  to  be  interfered  with 
for  obvious  reasons.  The  clearing-out  drops  are  mounted  at  the 
extreme  top  of  the  panels  and  are  numbered  to  correspond  with  the 
cord  circuits.  Directly  below  these  are  the  toll-line  drops,  numbered 
to  correspond  with  the  answering  jacks  beneath.  Five  toll  lines  per 
position  are  shown,  this  being  about  the  average  number  of  lines  that 
one  operator  can  handle.  It  is  impossible  to  make  any  definite  state- 
ment as  to  the  number  of  lines  that  ought  to  be  placed  in  one  position, 
this  being  regulated  entirely  by  local  conditions  and  operating  methods. 
The  toll-line  multiple  is  shown  next  below  the  line  drops;  it  is  good 
practice  to  place  a  designation  strip  immediately  above  the  jacks,  to 
facilitate  proper  numbering  of  the  lines. 

The  outgoing  trunks  to  the  various  local  offices  are  just  below  the 
toll  lines  and  are  multipled  across  the  board  in  a  similar  manner. 


108 


TOLL  TELEPHONE  PRACTICE 


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MULTIPLE-DROP  TOLL  SWITCHBOARDS 


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110  TOLL  TELEPHONE  PRACTICE 

The  drawing  shows  sixty  of  these  trunks,  which  number  at  first 
thought  might  seem  excessive,  but  this  matter  is  regulated  entirely  by 
the  volume  of  terminal  traffic  and,  to  some  extent,  by  the  operating 
methods.  It  is  broadly  true  that  the  number  of  lines,  of  every  kind, 
is  governed  by  the  maximum  demand  or  busy  hour. 

The  toll  answering  jacks  are  naturally  placed  at  the  bottom  of  the 
panel.  In  the  extreme  left  panel  of  each  position  are  shown  the 
switches  for  transferring  the  toll  lines  from  the  terminal  position  to 
the  night  or  common-drop  position.  The  office  and  interposition 
trunks  are  shown  in  the  middle  panel.  The  line  pilot,  the  super- 
visory pilot  and  the  interposition  trunk  lamps  are  located  in  the  pilot 
rail,  where  they  are  well  isolated  from  the  other  equipment  and  thus 
conspicuous.  It  will  be  noted  that  the  keyboard  has  been  designed 
with  sufficient  width  to  give  the  operator  plenty  of  room  for  handling 
tickets.  The  keys  have  been  grouped  in  a  manner  identical  with 
that  mentioned  in  Chapter  VI,  for  reasons  there  given.  The  cal- 
culagraph  is  mounted  in  the  space  between  the  two  operators  so 
as  to  be  readily  accessible  to  both.  A  messenger  key  is  shown  in 
the  front  rail  beneath  the  keyboard.  The  messenger  circuit  and  its 
operation  will  be  fully  explained  in  the  next  chapter.  The  top  part 
of  the  section  is  occupied  by  pigeon  holes  for  filing  toll  tickets. 

Fig.  51  shows  a  combined  recording  and  common-drop  (or  night) 
section.  During  the  daytime  this  section  is  used  for  recording,  while 
at  night  it  is  used  as  a  common-drop  section.  The  toll-line  drops  can 
be  transferred  to  this  section  by  means  of  the  night  switches  at  the 
terminal  sections.  It  will  be  observed  that  the  general  layout  of  the 
section"  is  similar  to  the  one  already  shown,  except  that  there  is  no 
regular  line  equipment  and  the  pigeon-hole  space  is  occupied  by  drops. 
The  second  panel  is  equipped  in  addition  with  a  strip  of  twenty  lamps 
and  jacks  for  recording  purposes.  This  type  of  section  is  very  service- 
able, since  it  is  adapted  for  the  recording  work  during  the  daytime 
and  the  line  work  at  night,  when  the  traffic  is  a  minimum. 


MULTIPLE-DROP  TOLL  SWITCHBOARDS 


ill 


CHAPTER  VIII 
MULTIPLE-LAMP  TOLL  SWITCHBOARDS 

THE  previous  chapters  have  covered  all  the  types  of  toll  board  equip- 
ment except  that  one  which  employs  lamp  signals  exclusively.  This 
type  forms  the  subject  of  the  present  chapter.  It  has  numerous 
advantages,  chief  among  which  are  the  diminished  labor  and  greater 
speed  of  handling  traffic,  compact  arrangement  of  panel  equipment, 
and  a  system  of  visual  busy  signals  without  unprotected  intervals. 

Three  separate  types  of  multiple-lamp  board  are  covered  in  the 
following  subject  matter,  namely,  the  American  Telephone  and  Tele- 
graph Company's  type,  the  Tri-state  Telephone  and  Telegraph 
Company's  type  and  that  of  the  United  States  Telephone  Company. 
Each  of  these  types  is  fully  explained  for  toll-to-local  and  local-to-toll 
connections.  The  other  class  of  connection,  from  toll-to-toll,  is  sub- 
stantially the  same  for  all  three  equipments,  at  least  in  its  essential 
features.  This  will  be  described  first,  therefore,  in  order  to  avoid 
repetition  and  also  to  condense  as  much  as  possible  the  subsequent 
descriptions,  which  are  somewhat  complicated  at  best. 

General  Type  of  Toll-to-Toll  Connection.  —  A  complete  connection 
of  this  type  is  shown  in  Fig.  53.  It  will  be  noted  that  the  general 
scheme  employed  in  the  line  circuit  is  similar  to  the  one  used  in  a 
common  battery  subscriber's  circuit,  since  the  essential  features  of 
both  are  the  line  and  cut-off  relays.  The  line  relay  is  normally 
bridged  across  the  line,  through  one  contact  of  the  cut-off  relay.  The 
function  of  the  latter,  obviously,  is  to  open  the  circuit  of  the  former 
when  the  line  is  in  use.  The  method  of  operation  may  be  described 
as  follows. 

An  incoming  toll-line  signal,  or  ring,  will  energize  winding  i  of  relay 
M,  thereby  drawing  up  its  armature  and  completing  three  local 
circuits  which  can  be  traced  as  follows.  The  first  one  commences  at 
the  ground  on  armature  2  of  relay  N  and  passes  by  way  of  the  break 
contact  to  the  armature  of  relay  M ,  and  then  through  the  line  lamp  to 
battery,  which  will  light  the  lamp.  The  second  circuit  follows  the 

112 


MULTIPLE-LAMP  TOLL   SWITCHBOARDS 


."3 


114  TOLL  TELEPHONE  PRACTICE 

same  route  to  the  make  contact  of  relay  M,  but  from  that  point  it  finds 
its  way  to  battery  through  winding  2  of  relay  M.  This  circuit  locks 
relay  If  in  an  operated  position  until  the  circuit  is  broken  by  the 
drawing  up  of  armature  2  on  the  cut-off  relay  N.  Thus  it  must  be 
obvious  that  when  a  subscriber  calls  over  the  toll  line,  a  single  turn  of 
the  generator  crank  will  lock  the  line  relay  M  by  means  of  winding  2 
and,  consequently,  give  a  permanent  line  signal  at  the  switchboard. 
The  third  circuit  completed  by  means  of  the  operation  of  the  line  relay 
is  the  one  containing  the  busy  lamps.  This  circuit  can  be  traced  to 
the  make  contact  of  the  line  relay  as  outlined  above,  from  there  to 
armature  3  of  relay  N  and  thence  through  the  busy  lamps  to  battery. 
Thus  all  the  busy  signals  associated  with  this  particular  line  will  be 
lighted.  These  busy  lamps  are  mounted  above  the  multiple  jacks  of 
each  line  and  will  light  as  soon  as  a  line  signal  is  received,  or  an 
operator  plugs  into  one  of  the  jacks;  they  will  remain  lighted  as  long 
as  the  line  is  busy.  It  follows,  therefore,  that  an  operator  can  see  at 
a  single  glance  whether  or  not  a  line  is  busy. 

Returning  to  the  description  of  the  operation,  we  find  that  the 
incoming  signal  has  lighted  the  line  lamp.  The  operator,  observing 
the  displayed  signal,  will  plug  into  the  answering  jack  associated  with 
the  lamp,  operate  her  listening  key  4  and  determine  what  is  desired. 
The  act  of  plugging  into  the  jack  will  close  a  circuit  from  the  battery 
connected  to  the  coil  of  relay  H,  over  the  sleeve  of  the  cord  and  the 
jack,  through  the  coil  of  cut-off  relay  N,  to  ground.  Thus  these  two 
relays  will  be  energized.  The  operation  of  relay  N  performs  several 
functions.  In  the  first  place,  the  attraction  of  armature  i  opens  the 
circuit  of  coil  i  of  relay  M,  which  was  bridged  across  the  line.  Secondly, 
the  attraction  of  armature  2  will  remove  the  ground  from  the  com- 
pleted circuits  which  were  established  by  the  actuation  of  relay  M\ 
as  a  result,  this  relay  will  be  released  and  the  line  lamp  will  be  extin- 
guished. The  busy  lamps  will  not  be  extinguished,  however,  because 
the  ground  connection  removed  by  the  attraction  of  armature  2  of 
relay  N  is  reestablished  by  the  attraction  of  armature  3  of  the  same 
relay. 

The  operator,  having  actuated  her  listening  key,  is  in  a  position  to 
converse  over  the  toll  line.  Upon  being  requested  for  a  connection 
to  another  toll  line,  she  will  note  the  condition  of  the  busy  lamp  and, 
if  the  line  is  idle,  she  will  plug  into  the  multiple  jack  with  the  calling 
plug  of  the  cord  in  use  and  ring  over  the  outgoing  line.  The  act  of 


MULTIPLE-LAMP  TOLL   SWITCHBOARDS  115 

plugging  into  the  second  line  will  complete  a  circuit  which  can  be 
traced  over  the  same  general  path  as  that  outlined  for  the  incoming 
call ;  this  involves  the  operation  of  the  cut-off  relay  K  in  the  outgoing 
line  and  relay  J  in  the  cord  circuit.  If  it  is  the  duty  of  this  operator 
to  time  the  connection,  she  will  proceed  accordingly  and  exercise 
careful  supervision;  if  not,  she  will  pay  no  further  attention  until  she 
receives  a  signal. 

When  the  conversation  is  completed,  disconnect  signals  may  be 
received  from  either  or  both  directions;  the  operation  of  the  cord 
supervisory  signals  will  be  identical  in  either  case.  Hence  the  opera- 
tion of  but  one  circuit  need  be  described.  The  circuit  from  the  out- 
going line  is  the  one  which  is  traced  in  the  following.  The  current 
from  the  incoming  signal  will  seek  a  path  over  the  tip  side  of  the  line 
to  the  tip  of  the  cord,  through  winding  2  of  relay  O,  to  the  ring  side 
of  the  cord  and  thence  back  to  the  ring  side  of  the  line.  Thus  relay 
O  will  be  actuated,  and  locked  in  that  position,  in  turn  lighting  the 
supervisory  lamp  and  giving  the  operator  a  disconnect  signal.  The 
relay  is  locked  by  means  of  a  circuit  that  can  be  traced  from  the 
ground  on  key  4,  to  the  armature  of  relay  O,  through  winding  i  of  the 
same  relay,  to  the  make  contact  and  armature  of  relay  /  and  then  to 
battery.  The  lamp  is  lighted  by  a  circuit  starting  at  the  ground  on 
key  4;  from  there  it  can  be  followed  to  the  armature  of  relay  0  and 
then  through  the  lamp  to  battery.  When  signals  come  in  from  each 
line,  the  operator  will  receive  a  double  disconnect,  thereby  indicating 
that  the  conversation  is  finished;  she  will  then  take  down  the  con- 
nection. The  withdrawal  of  the  plugs  will  open  at  both  ends  of  the 
cord  the  circuits  containing  the  cut-off  relays  N  and  K  and  the  cord 
relays  H  and  7,  and  therefore  these  relays  will  be  de -energized.  The 
release  of  the  armatures  of  cut-off  relays  N  and  K  will  extinguish  the 
busy  lamps,  while  the  return  of  the  armatures  of  relays  /  and  H  will 
open  the  locking  windings  of  relays  O  and  F  respectively;  as  a  con- 
sequence the  latter  relays  will  be  de-energized  and  the  supervisory 
lamps  will  be  extinguished.  Thus  the  apparatus  is  all  restored  to 
its  normal  condition  and  ready  for  another  connection. 

Before  leaving  this  class  of  connection,  attention  should  be  called 
to  the  fact  that  the  locking  windings  of  relays  F  and  0  each  obtain 
ground  from  the  break  contact  of  the  listening  key  4.  This  is  necessary 
in  order  that  the  operator  may  extinguish  the  supervisory  lamp  in 
case  it  is  lighted  by  an  incoming  signal,  without  withdrawing  the  plug 


Ii6  TOLL  TELEPHONE  PRACTICE 

from  the  line  jack.  In  explaining  this,  reference  will  be  made  to  the 
answering  end  of  the  cord  circuit  only. 

An  incoming  signal  will  lock  relay  F  and  thus  light  the  supervisory 
lamp,  as  previously  explained.  The  operator,  upon  seeing  this  signal, 
will  operate  the  listening  key  4  to  answer.  She  thereby  brings  about 
the  double  result,  first,  of  unlocking  relay  Ft  which  in  turn  extinguishes 
the  supervisory  lamp  due  to  the  opening  of  the  make  contact  at  key  4, 
and  second,  of  bridging  her  telephone  set  across  the  circuit.  When 
the  operator  restores  her  listening  key,  the  ground  is  again  connected 
to  the  make  contacts  of  relays  O  and  F,  in  preparation  for  further 
supervision. 

The  cord  circuit  shown  in  Fig.  53  is  adapted  for  toll-to-local  as  well 
as  for  toll-to-toll  connections  and  the  local  trunking  schemes  are  so 
designed  that  a  two-wire  trunk  can  be  used  without  sacrificing  the 
inherent  advantage  of  ringing  the  local  subscriber  from  the  toll  board. 
None  of  the  two- wire  trunking  systems  previously  described  were  de- 
signed to  accomplish  this  result.  This  operating  advantage  is  made 
possible  by  placing  the  repeating  coil  in  the  trunk  circuit  at  the  local 
board.  It  is  impossible  to  ring  through  this  coil,  but  the  ringing 
signals  are  automatically  repeated  at  the  local  office.  This  feature  is 
obtained,  however,  at  the  expense  of  great  complexity  in  the  trunk 
circuit ;  for  it  is  the  direct  result  of  the  successive  operation  of  a  series 
of  relays,  the  functions  of  which  will  be  explained  later  on. 

Furthermore,  as  the  line  and  cord  circuits  shown  in  Fig.  53  are 
applicable  to  practically  all  multiple-lamp  toll  boards  now  in  common 
use,  the  remainder  of  the  description  of  this  type  of  equipment  will 
be  devoted  to  the  trunking  systems.  The  design  of  these  systems 
varies  according  to  the  type  of  local  board  with  which  they  are  as- 
sociated. There  are  three  of  them  which  merit  a  full  description.  A 
thorough  understanding  of  the  principles  and  operations  of  each  will 
enable  one  to  comprehend  readily  all  others  which  may  be  encountered 
in  actual  practice,  since  the  essential  operating  features  of  this  type 
of  board  are  fully  covered.  In  the  subsequent  description,  the  system 
which  is  furnished  by  'the  Western  Electric  Company  is  considered 
first,  inasmuch  as  it  was  the  pioneer  development  in  this  class  of 
equipment  and  the  first  to  be  used  by  an  operating  company.  The 
lamp-signal  toll  circuits  designed  and  used  by  the  American  Telephone 
and  Telegraph  Company  have  been  taken  as  patterns  for  similar 
purposes  in  the  independent  field. 


MULTIPLE-LAMP  TOLL   SWITCHBOARDS  II? 

American  Telephone  and  Telegraph  Company's  Equipment 

(a)  Toll-to-Local  Connection.  —  A  complete  conventional  circuit 
of  a  toll-to-local  connection  through  a  Western  Electric  Company's 
No.  i  toll  board,  as  used  by  the  American  Telephone  and  Telegraph 
Company,  is  shown  in  Fig.  54.  It  will  be  observed  that  the  toll  cord 
circuit  shown  is  equipped  for  the  audible  busy  signal,  while  the  line 
is  furnished  with  the  visual  busy  signal.  The  toll  operator  answers  a 
lighted  line  signal  by  inserting  the  answering  plug  of  one  of  the  cord 
circuits.  Upon  ascertaining  that  a  local  subscriber  is  desired,  she 
will  communicate  with  the  toll  local  trunk  operator  by  means  of  an 
order  circuit,  informing  the  latter  of  the  local  number  desired  and 
obtaining  from  her  a  trunk  assignment.  The  trunk  operator  will  then 
test  the  multiple  jack  of  the  local  line  desired  and,  if  idle,  will  insert 
the  plug  of  the  trunk  assigned.  The  insertion  of  this  plug  will  close 
a  circuit  from  the  ground  at  the  cut-off  relay  A,  through  the  sleeve 
relay  E  in  the  toll  trunk,  to  battery.  This  will  operate  relay  E,  which 
in  turn  will  close  the  tip  strand  of  the  toll  trunk  and  will  also  close 
the  circuit  containing  the  disconnect  lamp;  this  will  light  the  lamp. 
However,  as  soon  as  the  toll  operator  inserts  the  toll  plug  in  the  jack 
of  the  trunk  assigned,  relay  G  will  operate,  thereby  opening  the  circuit 
containing  the  disconnect  lamp;  and  as  both  operators  will  insert  the 
plugs  at  practically  the  same  instant,  the  lamp,  in  actual  practice,  will 
be  in  circuit  for  such  a  short  interval  that  it  will  seldom  come  up  to. 
brilliance.  The  closing  of  the  circuit  that  causes  the  operation  of 
relay  G  will  be  explained  later  on. 

The  toll  operator,  upon  inserting  the  calling  plug  of  the  pair  of 
cords  used  to  answer  the  incoming  line  call  in  the  trunk  jack  will 
close  a  circuit  from  the  ground  on  the  5oo-ohm  resistance  coil,  over 
the  sleeve  strands  of  the  trunk  and  the  plug  and  thence  through  the 
coils  of  relays  L  and  M  to  battery.  The  completion  of  this  circuit 
will  operate  relay  L  and  close  the  tip  strand  of  the  cord  circuit.  Relay 
M ,  however,  will  not  operate  because  it  is  wound  to  a  resistance  of 
only  20  ohms  and  will  not,  therefore,  receive  enough  current  to  be 
actuated  when  in  circuit  with  the  ico-ohm  winding  of  relay  L  and  the 
5oo-ohm  resistance  coil.  The  act  of  inserting  the  toll  plug  will  close 
another  circuit,  which  can  be  traced  from  the  negative  side  of  battery 
attached  to  the  coil  of  relay  G,  by  way  of  the  break  contacts  of  the 
"  make-be  fore -break  "  springs  of  relay  H,  through  the  coil  of  relay  F 


n8 


TOLL  TELEPHONE  PRACTICE 


MULTIPLE-LAMP  TOLL  SWITCHBOARDS  119 

and  winding  2  of  the  repeating  coil,  over  the  tip  strands  of  the  trunk 
and  the  cord  circuits,  through  winding  2  of  relay  N  and  then  by  way 
of  the  ring  strands  of  the  cord  and  the  trunk  circuits,  through  winding 
4  of  the  repeating  coil  and  the  other  break  contact  of  the  make- 
before-break  contacts  of  relay  H,  to  the  5oo-ohm  resistance  coil  K 
and  finally  to  ground.  The  completion  of  this  circuit  will  operate 
relays  G  and  N,  while  relay  F  will  not  respond  because  it  is  wound 
only  to  20  ohms  and  will  not,  therefore,  receive  enough  current  through 
the  52o-ohm  winding  of  relay  N,  the  ico-ohm  winding  of  relay  G  and 
windings  2  and  4  of  the  repeating  coil.  The  operation  of  relay  ^V  will 
light  the  supervisory  lamp  in  the  toll  cord  circuit,  while  relay  G  will 
extinguish  the  disconnect  lamp  in  the  toll  trunk  as  previously  stated. 
The  toll  operator  is  now  ready  to  ring  the  local  subscriber.  The 
operation  of  the  ringing  key  K  will  close  a  circuit  that  can  be  followed 
from  the  ground  on  the  tip  spring  of  this  key,  over  the  tip  strand  of 
the  cord  and  the  trunk  circuits,  through  winding  2  of  the  repeating 
coil,  the  coil  of  relay  F,  the  break  contact  of  the  make-bef ore- 
break  contacts  of  relay  H,  and  the  coil  of  relay  G  to  battery.  The 
closing  of  this  circuit  will  cause  the  actuation  of  relay  F,  for  in  this 
case  the  ico-ohm  winding  of  relay  G  and  the  winding  2  of  the  repeating 
coil  are  the  only  resistances  in  series  with  the  2o-ohm  coil  of  relay  F; 
and  hence  this  relay  will  receive  enough  current  for  its  operation. 
The  operation  of  relay  F  will  break  the  tip  and  the  ring  strands  of  the 
trunk  and  connect  the  plug  end  of  the  latter  to  the  leads  from  the 
ringing  generator;  this  will  send  ringing  current  out  on  the  local 
subscriber's  line. 

It  will  be  observed,  therefore,  that  the  toll  operator  can  ring  the 
local  subscriber  at  will;  and  as  this  operator  is  usually  in  a  position 
to  devote  her  attention  to  a  few  calls  at  any  given  time,  she  will  ring 
the  local  subscriber  oftener,  if  he  is  slow  in  answering,  than  the  trunk 
operator  in  the  methods  described  in  the  previous  chapter.  The 
attendant  delays  in  establishing  a  connection  will  be  minimized  under 
the  present  method. 

When  the  local  subscriber  answers,  there  will  be  a  .flow  of  current 
from  ground  through  winding  i  of  relay  H  and  winding  i  of  the 
repeating  coil,  to  the  tip  strand  of  the  trunk  and  the  line  circuits, 
through  the  subscriber's  instrument  and  back  by  way  of  the  ring 
strands  of  the  line  and  the  trunk  circuits,  through  winding  3  of  the 
repeating  coil,  winding  2  of  relay  H  and  the  make  contact  of  relay  G 


120  TOLL  TELEPHONE  PRACTICE 

to  battery.  Therefore  relay  H  will  operate  and  actuate  the  two  sets 
of  make-bef ore-break  springs.  The  operation  of  the  set  of  springs 
numbered  i  in  the  figure  will  first  close  a  circuit  which  can  be  traced 
from  ground  through  the  5oo-ohm  resistance  coil  K,  to  the  make 
contact  of  these  springs  and  then  by  way  of  the  coil  of  relay  G  to 
battery.  Immediately  after  the  making  of  the  contact  in  this  set 
of  springs,  the  break  contact  will  be  operated,  thus  opening  the  through 
ringing  circuit  which  traverses  the  coil  of  relay  F,  as  previously  traced. 
The  make  contact  in  this  set  of  springs  must  be  closed  before  the 
break  contact  in  the  other  set  is  opened,  so  as  to  prevent  a  momentary 
release  of  relay  G.  This  feature  is  essential  to  prevent  the  flashing 
of  the  disconnect  lamp  in  the  toll  trunk  circuit,  which  would  happen 
should  relay  G  be  de-energized.  The  operation  of  the  make  contact  of 
the  make-before-break  spring  in  set  2  closes  the  connection  between 
windings  2  and  4  of  the  repeating  coil  and  thus  completes  the  talking 
circuit  of  this  end  of  the  trunk,  which  is  normally  open;  while  the 
opening  of  the  break  contact  of  this  set  of  springs  opens  the  circuit 
containing  winding  2  of  relay  N  (in  the  toll  cord)  at  the  ground  con- 
nection and  thus  causes  the  release  of  this  relay.  The  latter  will  open 
the  supervisory  lamp  circuit  and  thus  inform  the  toll  operator  that 
the  local  subscriber  has  answered.  The  toll  operator  will  then  proceed 
to  complete  the  connection. 

When  the  conversation  is  finished  the  incoming  signal  from  the  toll 
line  will  light  the  answering  supervisory  lamp  in  the  cord  circuit. 
The  local  subscriber  will  hang  up  his  receiver  and  thus  open  the  circuit 
containing  relay  H\  the  sets  of  springs  numbered  i  and  2  will  return 
to  their  normal  position,  which  is  required  to  close  the  circuit  con- 
taining winding  2  of  relay  N.  This  relay  will  light  the  calling  super- 
visory lamp  in  the  toll  cord  circuit.  The  toll  operator,  upon  seeing 
these  disconnect  signals,  will  take  down  the  connections.  The  with- 
drawal of  the  calling  plug  from  the  trunk  multiple  jack  will  de -energize 
relay  G  and  thus  light  the  disconnect  lamp  at  the  local  trunking 
position;  this  gives  the  trunking  operator  the  disconnect  signal.  She 
will  then  take  down  the  connection  and  thereby  restore  the  apparatus 
to  its  normal  condition. 

Before  leaving  this  particular  circuit  it  seems  advisable  to  call 
attention  to  the  two  battery  voltages  that  are  employed.  It  will  be 
noticed  that  the  local  end  of  the  trunk  is  equipped  with  a  48-volt 
battery,  while  the  remainder  of  the  circuit  operates  from  a  24-volt 


MULTIPLE-LAMP  TOLL   SWITCHBOARDS  121 

battery.  This  48-volt  battery  at  the  local  end  will  increase  the  current 
through  the  subscriber's  transmitter  and  thus  materially  improve  the 
transmission. 

(b)  Local-to-Toll  Connection.  —  A  complete  conventional  recording 
circuit  used  with  the  Western  Electric  Company's  No.  i  multiple-lamp 
toll  board  is  shown  in  Fig.  55,  to  which  reference  will  be  made  in  the 
ensuing  description.  A  local  subscriber  who  desires  toll  service  will 
call  the  office  in  the  usual  manner.  The  local  operator  will  then 
transfer  the  call  to  a  recording  operator.  This  is  accomplished  by 
means  of  a  special  cord  known  as  "  the  tone-test  cord,"  two  of  which 
are  installed  in  each  local  operator's  position.  When  the  local  operator 
determines  that  a  toll  connection  is  desired,  she  will  test  the  multiple 
jack  of  one  of  the  recording  trunks  with  the  calling  plug  of  the  pair 
of  cords  just  used  to  answer  the  call.  'Upon  finding  an  idle  trunk  she 
will  insert  the  calling  plug  of  one  of  the  tone-test  cord  circuits  in  the 
jack  of  the  idle  trunk  line  and  will  also  insert  the  answering  plug  of 
the  tone-test  cord  circuit  in  the  multiple  jack  of  the  calling  subscriber's 
line,  removing  the  answering  plug  which  was  originally  inserted  in  the 
answering  jack  in  response  to  the  call.  The  local  operator  is  now 
relieved  of  all  further  work  in  the  establishment  of  the  connection, 
since  she  simply  obeys  the  disconnect  signals  in  the  tone-test  cord 
circuit;  the  local  subscriber  has  been  switched  to  a  recording  position 
at  the  toll  board.  By  referring  to  Fig.  55  it  will  be  observed  that  the 
tone-test  cord  circuit  is  equipped  with  double  supervision.  The  act 
of  inserting  the  answering  plug  of  this  cord  circuit  in  the  multiple 
jack  of  the  subscriber's  line  will  not  light  the  white  supervisory 
lamp,  because  the  subscriber  has  his  receiver  off  the  hook;  relay  E, 
therefore,  is  energized  and  the  lamp  is  shunted  by  a  low  resistance. 
The  insertion  of  the  plug,  however,  will  place  a  tone  signal  on  all 
the  multiple  jacks  associated  with  this  line;  and  thus  should  another 
operator  test  the  line,  she  will  be  informed  by  the  tone-test  that  the 
line  is  being  held  for  toll  service.  The  tone -test  is  a  low  alternating 
potential  placed  on  the  sleeve  of  the  tone-test  plug,  by  means  of  the 
interrupter  and  the  step-down  transformer  shown  in  the  circuit. 
This  potential  reaches  the  sleeve  of  the  line  by  means  of  a  path  that 
can  be  traced  from  battery,  through  the  low  winding.of  the  transformer, 
to  the  make  contact  and  armature  of  relay  £;  and  then  by  way  of  the 
resistance  coils  H  and  G,  the  sleeve  of  the  cord  and  plug,  the  sleeve 
of  the  multiple  jack,  and  the  coil  of  the  cut-off  relay  to  ground.  An 


122 


TOLL  TELEPHONE  PRACTICE 


MULTIPLE-LAMP  TOLL  SWITCHBOARDS  123 

alternating  potential  is  impressed  on  the  circuit  thus  completed,  due 
to  the  pulsating  current  from  the  interrupter  which  flows  through  the 
primary  of  the  transformer  and  acts  inductively  on  the  low-wound 
secondary.  Thus  an  operator,  in  testing  a  line  on  the  sleeve  of  which 
this  potential  exists,  will  receive,  instead  of  the  customary  busy  click, 
a  note  or  hum,  the  pitch  of  which  will  depend  upon  the  rapidity 
of  the  interruptions.  It  is  necessary  to  use  the  transformer  because 
a  direct  connection  with  the  interrupter  would  produce  a  very  loud 
note  of  exceedingly  harsh  quality. 

It  has  been  pointed  out  that  the  white  lamp  associated  with  the 
answering  plug  of  the  tone-test  cord  will  not  light  and  this  is  true  also 
of  the  red  lamp  associated  with  the  calling  plug.  When  the  operator 
inserts  this  plug  in  the  jack  of  the  recording  trunk  circuit,  the  only 
signaling  circuit  closed  is  the  one  from  battery  through  the  resistance 
coil  L,  to  the  break  contact  and  armature  i  of  relay  M,  the  sleeve  of 
the  cord  and  the  recording  trunk  circuit,  through  the  winding  of  relay 
P  to  ground.  Relay  P  is  thus  energized  and  will  light  a  lamp  at  the 
recording  operator's  position  which  is  associated  with  the  trunk.  The 
recording  operator,  upon  seeing  this  signal  displayed,  will  insert  the 
plug  of  one  of  her  cord  circuits  in  the  jack  of  the  trunk.  The  act  of 
inserting  the  plug  of  the  recording  cord  will  not  cause  any  change  in 
the  condition  of  the  apparatus,  but  the  operation  of  the  listening  key 
will  cause  a  flow  of  current  from  the  negative  side  of  the  battery 
through  winding  4  of  the  repeating  coil,  the  winding  of  relay  N  and 
then  over  the  ring  strands  of  the  cord  and  the  trunk,  through  winding 
2  of  relay  R,  over  the  ring  strand  of  the  recording  trunk  and  cord 
circuit,  through  the  winding  of  relay  X  and  then  by  way  of  the  tip 
strand  of  the  recording  cord  and  trunk  and  the  tone-test  cord,  through 
winding  2  of  the  repeating  coil  and  finally  to  ground.  Thus  relay  X 
in  the  recording  cord  circuit,  relay  R  in  the  recording  trunk  circuit 
and  relay  N  in  the  tone-test  cord  circuit  will  be  energized.  The 
operation  of  relay  X  will  place  a  4O-ohm  shunt  around  the  "  holding 
lamp  "  in  the  recording  cord  circuit,  and  therefore  this  lamp  will  not 
light  when  the  listening  key  is  actuated.  The  operation  of  relay  R 
will  open  the  circuit  containing  the  lighted  lamp  in  the  recording  trunk, 
and  this  lamp,  consequently,  will  be  extinguished;  this  relay  is  self- 
locking  and  thus  prevents  the  re -lighting  of  the  recording  trunk  lamp. 
This  locking  circuit  can  be  traced  (bearing  in  mind  that  relay  P  has 
been  previously  operated)  from  the  ground  on  the  armature  of  relay 


124  TOLL  TELEPHONE  PRACTICE 

Pj  through  the  make  contact  of  this  relay,  and  the  armature,  make 
contact  and  winding  i  of  relay  R,  to  the  sleeve  of  the  trunk  and  tone- 
test  cord  circuits,  then  through  the  winding  of  relay  M,  the  armature 
and  make  contact  of  relay  N  (previously  operated),  through  the  40- 
ohm  resistance  coil  to  battery.  Relay  M  is  thus  energized  and  will 
close  a  circuit  from  the  battery  in  the  tone- test  cord,  through  the  red 
lamp,  armature  2,  the  make  contact  and  coil  of  relay  M,  the  sleeve 
strand  of  the  tone-test  cord,  the  recording  trunk  circuit  and  through 
the  winding  of  relay  P  to  ground.  The  red  lamp  contained  in  the 
circuit  just  completed  will  not  light,  however,  due  to  the  shunting 
action  of  the  40-ohm  resistance  coil  O,  which  is  placed  in  parallel  with 
the  lamp  by  the  armature  contacts  of  relay  N.  The  recording  con- 
nection has  now  been  traced  to  a  point  where  the  recording  operator 
is  in  a  position  to  converse  with  the  local  subscriber  and  all  the  signals 
in  the  connection  are  extinguished.  The  recording  operator  will  now 
obtain  from  the  local  subscriber  the  information  required  to  make 
out  the  regular  toll  ticket.  After  this  the  operator  has  two  methods 
of  procedure  at  her  disposal,  the  choice  between  them  depending 
upon  whether  or  not  she  has  reason  to  believe  that  the  connection 
can  be  completed  with  little  delay.  In  case  she  thinks  that  it  will 
take  considerable  time  to  establish  the  connection,  she  will  tell  the 
local  subscriber  to  hang  up  his  receiver  and  wait  until  he  is  called. 
The  act  of  hanging  up  the  receiver  will  open  the  circuit  containing 
relay  E  in  the  tone-test  cord,  thus  releasing  the  relay  and  thereby 
removing  the  shunt  around  the  white  disconnect  lamp,  which  will 
then  be  displayed.  The  local  operator  will  not  heed  this  signal,  how- 
ever, as  the  red  disconnect  lamp  is  the  governing  signal  upon  which 
the  removal  of  the  connection  depends.  The  recording  operator, 
having  told  the  subscriber  to  hang  up  his  receiver,  will  pass  the  toll 
ticket  to  a  line  operator  and  remove  the  plug  from  the  recording  trunk 
jack.  The  withdrawal  of  the  plug  will  open  the  circuit  containing 
relay  N,  which  was  previously  traced.  The  release  of  this  relay  will 
remove  the  shunt  circuit  around  the  red  disconnect  lamp  in  the  tone- 
test  cord  and  this  lamp  will  be  lighted.  The  lighting  of  the  lamp 
signifies  to  the  local  operator  that  the  recording  operator  is  through 
with  the  connection  and  the  former  will  clear  the  same.  As  the  toll 
ticket  is  now  in  the  hands  of  the  regular  line  operator,  she  will  take 
care  of  the  connection,  the  recording  operator  having  nothing  further 
to  do  with  it. 


MULTIPLE-LAMP  TOLL  SWITCHBOARDS  125 

However,  when  the  recording  operator,  upon  making  out  the  toll 
ticket,  has  good  reason  to  believe  that  the  toll  connection  can  be 
established  at  once,  the  procedure  is  different.  In  this  case,  she  will 
place  herself  in  communication  with  the  trunking  operator  at  the  local 
board  and  ask  for  a  trunk  assignment.  Thereupon,  the  trunk  operator 
will  assign  a  trunk  and  pass  the  number  to  the  recording  operator 
who  will  place  it  upon  the  toll  ticket.  The  trunk  operator,  in  the 
meantime,  will  test  the  multiple  jack  of  the  local  line  and  find  the 
tone-test  due  to  the  presence  of  the  tone-test  cord  in  the  multiple  jack 


Alternating-current  Relay. 

at  the  answering  operator's  position.  The  trunk  operator  will  insert 
the  trunk  plug  in  the  multiple  jack  of  the  local  line.  The  recording 
operator  will  withdraw  the  plug  from  the  recording  trunk  and  insert 
it  in  the  multiple  jack  of  the  assigned  trunk.  The  withdrawal  of  this 
plug  will  give  the  answering  operator  the  disconnect  at  the  tone-test 
cords,  as  in  the  previous  case.  The  recording  operator,  upon  inserting 
the  plug  in  the  multiple  jack  of  the  assigned  trunk,  will  be  able  to 
communicate  with  the  local  subscriber  and  thus  assure  herself  that 
the  connection  has  been  properly  completed.  She  will  then  pass  the 
toll  ticket  to  the  proper  line  operator.  Should  the  subscriber  desire 
to  signal  the  recording  operator,  he  can  do  so  by  actuating  his  receiver 
hook,  which  will  make  and  break  the  circuit  through  the  coil  of  relay 
X,  and  in  turn  make  and  break  the  shunt  around  the  holding  lamp  in 
the  recording  cord  circuit;  this  will  flash  the  lamp  and  attract  the 
operator's  attention. 

The  operation  of  this  system  has  now  been  traced  to  the  point  where 
the  line  operator  takes  up  the  connection.  This  operator,  upon  re- 
ceiving the  toll  ticket,  will  know  immediately  whether  or  not  the 
local  trunk  for  the  connection  has  been  assigned,  by  an  inspection  of 
the  ticket.  In  case  no  trunk  assignment  has  been  placed  on  the  ticket, 
she  will  know  that  the  trunk  has  not  been  assigned  and  that  the  calling 


126  TOLL  TELEPHONE  PRACTICE 

subscriber  is  not  waiting  on  the  line.  In  the  last  case,  she  will  proceed 
to  obtain  the  distant  subscriber  desired.  When  this  subscriber  has  been 
secured,  she  will  put  up  the  rest  of  the  connection  in  a  manner  identical 
with  that  previously  described  for  the  toll-to-local  connection. 

In  the  first  case,  when  the  toll  operator  sees  the  trunk  assignment 
on  the  ticket,  she  knows  the  recording  operator  has  ordered  up  the 
connection  and  that  the  local  subscriber  is  waiting  on  the  line.  Under 
these  circumstances  she  will  first  insert  the  answering  plug  of  one  of 
the  cord  circuits  in  the  multiple  jack  of  the  assigned  trunk  and 
then  insert  the  calling  plug  in  the  toll  line  and  complete  the  con- 
nection at  once,  if  possible.  If  a  delay  is  unavoidable  she  will  tell 
the  local  subscriber  to  hang  up  his  receiver  and  wait  until  called.  The 
act  of  inserting  the  answering  plug  in  the  assigned  trunk  jack  will  close 
a  circuit  that  can  be  traced  from  the  ground  through  the  winding  of 
relay  T  in  the  recording  operator's  cord  circuit,  t$  the  sleeve  of  the 
toll  operator's  cord  circuit  and  through  the  windings  of  relays  L  and  M 
to  battery.  This  will  operate  relay  T,  thereby  lighting  the  disconnect 
lamp  in  the  recording  operator's  cord  circuit.  The  lighting  of  this 
lamp  will  inform  the  recording  operator  that  the  line  operator  has 
taken  up  the  connection  and  the  former,  therefore,  will  take  down  the 
connections  at  her  position. 

Another  incoming  ring-through  trunk  circuit  used  by  the  American 
Telephone  and  Telegraph  Company  in  connection  with  the  Western 
Electric  Company's  No.  i  type  toll  switchboard  is  shown  in  Fig.  56. 
In  this  circuit  a  different  scheme  is  used  to  ring  around  the  repeating 
coil.  The  circuit  also  shows  the  method  of  equipping  these  trunks 
when  party-line  service  is  given,  by  means  of  which  the  local  trunk 
operator  selects  the  proper  ringing  current  required  to  call  the  desired 
party-line  subscriber.  The  work  of  the  line  operator  in  ringing  a 
party-line  subscriber  is  consequently  identical  with  that  required  to 
ring  a  direct-line  subscriber.  Due  to  the  special  features  that  are 
contained  in  this  circuit,  a  description  of  its  operation  will  probably 
be  of  value.  In  following  the  description  of  this  circuit  it  should  be 
remembered  that  it  operates  in  conjunction  with  the  circuits  shown  in 
Fig.  54  and  replaces  the  trunk  circuit  in  that  diagram. 

The  toll -line  operator  will  communicate  with  the  local  trunk  operator 
by  means  of  an  order  circuit  and  obtain  a  trunk  assignment  as  before. 
The  trunk  operator  will  then  test  the  local  line;  in  case  it  is  idle,  she 
will  assign  the  trunk  and  insert  the  trunk  plug  in  the  multiple  jack. 


MULTIPLE-LAMP  TOLL  SWITCHBOARDS 


127 


This  operation  will  complete  a  circuit  from  the  ground  at  the  cut-off 
relay,  by  way  of  the  sleeve  conductor  of  the  jack  and  the  trunk,  through 
the  winding  of  relay  E  and  the  trunk  lamp  to  battery.  This  will  light 
the  disconnect  lamp  in  the  trunk  circuit  and  also  cause  the  operation 
of  relay  E,  which  in  turn  will  close  the  tip  strand  of  the  trunk  circuit. 
In  the  meantime,  however,  the  toll  operator  will  have  inserted  the 
calling  cord  in  the  trunk  jack  assigned  by  the  trunk  operator.  This 
will  have  completed  a  circuit  from  battery  through  winding  2  of  relay 
G,  by  way  of  the  make-before-break  spring  2  of  relay  C,  winding 


TOLL 
Sw.  Bo. 


FIG.  56.  —  Incoming  Toll  Trunk  of  the  American  Telephone  and  Telegraph  Company's 
Type,  Showing  Four-party  Through  Ringing. 

3  of  the  repeating  coil,  the  ring  strand  of  the  trunk  and  the  toll  cord, 
through  the  bridged  winding  of  the  supervisory  relay,  the  tip  side  of 
the  cord  and  the  trunk,  winding  i  of  the  repeating  coil,  the  make-before- 
break  contact  i  of  relay  C  and  then  by  way  of  winding  i  of  relay  G 
to  ground.  The  completion  of  this  circuit  will  cause  the  operation  of 
the  supervisory  relay  in  the  cord,  thereby  lighting  the  supervisory 
lamp ;  and  it  will  also  cause  the  operation  of  relay  G.  The  operation 
of  the  latter  will  extinguish  the  trunk  lamp  that  was  previously  lighted 
by  the  insertion  of  the  trunk  plug;  and  as  the  toll-line  operator  and  the 
trunk  operator  will  complete  their  connections  at  practically  the  same 
time,  the  trunk  lamp  will  seldom  respond.  The  circuit  that  "shunts 
out"  the  disconnect  lamp  can  be  traced  from  the  battery  on  the 


128  TOLL  TELEPHONE  PRACTICE 

make  contact  of  relay  G,  by  way  of  the  armature  of  this  relay,  to  arma- 
ture 2  of  relay  E,  and  then  (bearing  in  mind  that  this  relay  was  operated 
the  instant  the  trunk  plug  was  inserted)  by  way  of  the  make  contact 
and  the  40-ohm  resistance  coil,  the  winding  of  relay  E  and  the  sleeve 
of  the  trunk  and  the  local  line,  to  the  ground  on  the  winding  of  the 
cut-off  relay.  In  case  the  toll  operator  puts  up  her  end  of  the  con- 
nection first,  the  disconnect  lamp  in  the  trunk  circuit  will  light,  and 
remain  lighted  until  the  trunk  operator  puts  up  the  other  end  of  the 
connection.  When  the  toll  operator  inserts  the  plug  in  the  assigned 
trunk  jack,  relay  G,  as  we  have  seen,  will  be  operated.  This  will 
complete  a  circuit  from  the  battery  connection  on  the  make  contact 
of  that  relay  to  its  armature  and  then,  remembering  that  relay  E  is 
inactive,  by  way  of  the  armature  and  break  contact  of  this  relay,  to 
the  coil  of  relay  D  and  coil  i  of  relay  G  to  ground.  The  establishment 
of  this  circuit  will  lock  relay  G  until  relay  E  is  energized;  it  will  also 
energize  relay  Z),  which  in  turn  will  light  the  disconnect  lamp  in  the 
trunk  circuit.  Therefore,  since  relay  G  is  locked  until  relay  E  is 
energized,  the  disconnect  lamp  in  the  trunk  will  remain  lighted  until 
the  trunk  operator  puts  up  the  connection,  even  though  the  toll 
operator  should  withdraw  the  toll  plug  from  the  assigned  trunk  jack. 

The  local  trunk  operator's  work  in  putting  up  a  connection  with  a 
direct-line  subscriber  consists  merely  of  inserting  the  trunk  plug  into 
the  multiple  jack  of  the  line.  When  a  party-line  subscriber  is  desired, 
however,  the  trunk  operator, '  after  inserting  the  plug,  must  set  the 
ringing  key  to  call  the  proper  subscriber.  When  this  key  is  depressed 
it  will  be  held  in  the  operated  position  by  the  coil  of  the  magnetic 
clutch,  which  is  energized  when  the  trunk  plug  is  inserted,  by  means 
of  a  circuit  traceable  from  the  ground  on  the  coil  of  the  cut-off  relay, 
by  way  of  the  sleeve  strand  of  the  local  line  and  the  plug,  through  the 
clutch  coil  to  battery.  The  selective  ringing  buttons  in  this  key  will 
remain  depressed  until  they  are  released  by  the  demagnetization  of 
the  clutch  coil,  upon  the  withdrawal  of  the  plug. 

The  toll  operator  is  now  ready  to  ring  the  local  subscriber.  She 
will  next  operate  the  ringing  key,  which  will  send  alternating  current 
over  the  trunk  circuit  to  the  local  office.  This  current  will  energize 
relay  H  and  thus  complete  a  circuit  that  may  be  traced  from  the 
battery  connection  on  the  make  contact  of  this  relay,  by  way  of  its 
armature,  to  the  coils  of  relays  F  and  C  and  thence  to  ground.  This 
will  energize  these  two  relays.  The  operation  of  relay  F  will  be 


MULTIPLE-LAMP  TOLL   SWITCHBOARDS  129 

equivalent  to  actuating  the  ringing  key  at  the  trunk  position,  for  the 
make  contacts  of  this  relay  are  connected  to  the  source  of  ringing 
current,  and  the  break  contacts  will  cut  off  the  switchboard  end  of 
the  trunk,  to  prevent  ringing  back  over  the  circuit  in  the  direction  of 
the  toll  office.  The  operation  of  relay  C  will  open  the  circuit  which 
feeds  current  through  windings  i  and  2  of  relay  G  to  the  toll  end  of  the 
trunk  circuit,  thus  disconnecting  the  battery  from  this  part  of  the 
circuit  while  the  toll  operator  is  ringing.  The  opening  of  this  circuit 
will  not  cause  the  release  of  relay  G,  however,  as  the  path  through 
the  toll  end  of  the  trunk  is  substituted  by  the  make-before-break 
contacts  at  relay  C.  It  is  thus  obvious  that  the  operation  of  relay 
F  will  ring  the  subscriber,  and  as  the  actuation  of  this  relay  is  under 
the  control  of  the  toll  operator,  she  can  ring  at  will.  When  the  local 
subscriber  answers,  thereby  bridging  his  telephone  set  across  the  line, 
current  will  flow  over  the  tip  strand  of  the  trunk  and  the  line  circuit, 
through  the  subscriber's  instrument,  back  over  the  ring  side  of  the 
line  and  the  trunk  and  thence  through  the  coil  of  relay  J  to  battery. 
Relay  /  will  thus  be  energized  and  will  close  a  circuit  from  the  battery 
connection  on  the  make  contact  of  relay  G,  to  the  armature  of  this 
relay,  then  by  way  of  the  armature  and  make  contact  of  relay  /  and 
the  coil  of  relay  C  to  ground.  Relay  C  will  consequently  operate  and 
attract  the  make-before-break  springs  i  and  2.  The  contacts  of 
these  two  sets  of  springs  will  maintain  the  circuit  through  the  coils 
of  relay  G,  which  was  previously  closed  through  the  bridged  winding 
of  the  supervisory  relay  in  the  toll  cord ;  the  trunk  portion  of  this  cir- 
cuit is  cut  off  by  the  operation  of  the  break  contacts  of  the  two  sets 
of  springs.  The  opening  of  the  circuit  through  the  bridged  winding 
of  the  supervisory  relay  in  the  toll  cord  circuit  will  extinguish  the 
supervisory  lamp.  This  will  notify  the  toll  operator  that  the  local 
subscriber  has  answered.  She  will  then  proceed  with  the  connection 
as  previously  outlined. 

When  the  toll  conversation  is  finished  the  disconnect  signal  from 
the  local  subscriber  will  be  received  in  the  manner  next  described. 
The  subscriber,  upon  hanging  up  his  receiver,  will  open  the  line  circuit 
and  thereby  release  relay  /.  This  in  turn  will  de -energize  relay  C. 
Restoring  relay  C  to  its  normal  condition  will  again  feed  current  from 
the  local  office  over  the  trunk  circuit  and  thence  through  the  bridged 
winding  of  the  supervisory  relay  in  the  toll  cord  circuit.  This  relay 
will  give  the  toll  operator  the  disconnect  signal,  and  she  will  take  down 


130  TOLL  TELEPHONE  PRACTICE 

the  connection.  The  removal  of  the  connection  at  the  toll  board  will 
de -energize  relay  G,  which  in  turn  will  remove  the  shunt  circuit  (pre- 
viously traced)  around  the  disconnect  lamp.  This  lamp  will  then 
light,  thereby  giving  the  local  trunk  operator  a  disconnect  signal, 
whereupon  she  will  take  down  the  connection  and  restore  the  appara- 
tus, to  its  normal  condition. 

Tri-state  Telephone  and  -Telegraph  Company's  Equipment 

(a)  Toll-to-Local  Connection.  —  The  circuits  that  have  been  de- 
scribed thus  far,  in  connection  with  the  multiple-lamp  toll  board,  out- 
line one  of  the  practices  of  the  American  Telephone  and  Telegraph 
Company  and  constitute  one  of  the  three  general  systems  previously 
referred  to.  The  second  general  type  which  we  shall  now  consider  is 
the  system  used  by  the  Tri-state  Telephone  and  Telegraph  Company 
in  their  toll  office  at  St.  Paul,  Minn.;  a  view  of  the  switchboard  is 
shown  in  Fig.  57.  This  system  was  installed  by  the  Kellogg  Switch- 
board and  Supply  Company  and  operates  with  the  Stromberg-Carlson 
local  boards  at  Minneapolis  and  St.  Paul.  The  local  boards  are 
equipped  with  what,  practically  speaking,  is  a  two-wire  system,  since 
the  sleeve  and  ring  conductors  are  short-circuited  by  the  ring  of  the 
plug.  A  conventional  diagram  of  the  toll-to-local  connection  for  this 
type  of  equipment  is  shown  in  Fig.  58,  the  operation  of  which  will  be 
explained  briefly  in  the  following. 

When  the  toll  operator  receives  an  inward  toll  call,  she  will  com- 
municate with  the  local  trunk  operator  and  ask  for  a  trunk  assignment. 
The  trunk  operator,  thereupon,  will  select  a  trunk,  operate  the  testing 
key  and  test  the  multiple  jack  of  the  local  line  called  for.  In  case  the 
line  is  idle,  she  will  plug  into  the  jack  and  restore  the  testing  key  to 
normal.  This  will  close  a  circuit  from  the  ground  on  winding  i  of  the 
cut-off  relay,  by  way  of  the  tip  strands  of  the  line  and  the  trunk 
circuits,  through  the  winding  of  relay  L  to  battery.  Relays  L  and 
Q  are  consequently  energized.  The  attraction  of  armature  i  of  relay 
L  will  complete  a  circuit  that  can  be  traced  from  the  ground  on  the 
disconnect  lamp,  to  the  armatures  and  break  contacts  of  relays  M  and 
K  and  the  make  contact  and  armature  i  of  relay  L  to  battery.  The 
completion  of  this  circuit  will  light  the  disconnect  lamp.  In  the 
meantime,  however,  the  toll  operator  will  have  received  the  assignment 
and  inserted  the  calling  plug  in  the  trunk  jack.  This  will  complete 
a  circuit  which  is  traceable  from  the  battery  on  the  coil  of  relay  5,  by 


MULTIPLE-LAMP  TOLL   SWITCHBOARDS 


132  TOLL  TELEPHONE  PRACTICE 

way  of  the  make  contact  and  armature  2  of  relay  Z,,  the  coil  of  relay 
M,  the  break  contact  and  armature  i  of  relay  H,  to  the  tip  strand  of 
the  trunk  circuit,  thence  over  the  tip  strand  of  the  toll  cord  circuit, 
through  winding  i  of  relay  F  to  the  ring  strand  of  the  toll  cord ;  from 
there  it  can  be  followed  over  the  ring  strand  of  the  trunk  circuit  to 
armature  2  and  the  break  contact  of  relay  H  and  through  retardation 
coil  /  to  ground.  Relays  M  and  F  will  thereupon  operate,  while 
relay  6*  will  remain  normal,  -due  to  the  fact  that  it  is  low- wound  and 
will  not  receive  sufficient  current  to  operate  when  in  series  with  all 
the  resistances  that  are  contained  in  the  circuit  just  outlined.  How- 
ever, due  to  the  operation  of  relay  M,  the  disconnect  lamp  in  the  trunk 
circuit  will  be  extinguished,  whereas  the  operation  of  relay  F  will 


A  Strip  of  Twenty  Visual  Busy  Signals. 

light  the  supervisory  lamp  in  the  toll  cord.  The  connection  has  now 
been  traced  to  the  point  where  the  toll  operator  is  ready  to  ring  the 
local  subscriber.  The  act  of  ringing  will  close  a  circuit  traceable  from 
the  ground  on  the  tip  spring  of  the  ringing  key,  by  way  of  the  tip 
strands  of  the  cord  and  the  trunk,  to  armature  i  and  the  break  contact 
of  relay  H,  then  through  the  winding  of  relay  M,  armature  2  and  the 
make  contact  of  relay  L  and  the  winding  of  relay  5*  to  battery.  It 
will  be  noted  that  this  circuit  follows  the  same  path  to  the  tip  of  the 
ringing  key  as  the  former  circuit  containing  relay  S,  which  was  com- 
pleted when  the  toll  operator  inserted  the  plug.  However,  the  latter 
circuit  contains  less  series  resistance  by  the  amount  of  winding  i  of 
relay  F,  winding  3  of  the  repeating  coil  and  the  winding  of  retardation 
coil  /,  because  it  passes  to  ground  at  the  make  contact  of  the  ringing 
key,  whereas  the  other  circuit  was  completed  to  ground  at  the  retarda- 
tion coil  J.  An  increased  amount  of  current  will  consequently  flow 
through  the  winding  of  relay  S,  which  will  therefore  be  actuated. 
Then  as  the  make  contacts  of  this  relay  are  wired  to  the  source  of 
ringing  current,  the  operation  of  the  ringing  key  in  the  toll  cord  circuit 
will  ring  the  local  subscriber  in  the  same  manner  as  described  in  the 
last  two  circuits. 

The  local  subscriber,  upon  answering  the  call,  will  complete  a  circuit 


MULTIPLE-LAMP  TOLL   SWITCHBOARDS 


133 


134  TOLL  TELEPHONE  PRACTICE 

which  is  traceable  from  the  battery  on  the  coil  of  relay  K,  by  way  of 
the  ring  strands  of  the  trunk  and  the  line  circuits,  through  the  sub- 
scriber's instrument,  returning  over  the  tip  of  the  line  and  through  the 
coil  of  the  cut-off  relay  Q  to  ground.  Relay  K  will  subsequently 
operate  and  close  a  circuit  that  is  traceable  from  the  battery  on  arma- 
ture i  of  relay  L,  to  the  make  contact  of  this  relay,  over  the  armature 
and  make  contact  of  relay  K  and  thence  through  the  coil  of  relay  H 
to  ground.  Relay  H,  therefore,  will  operate  and  open  the  circuit 
previously  traced  which  contains  the  supervisory  lamp  in  the  toll  cord ; 
this  will  inform  the  toll  operator  that  the  local  subscriber  has  answered. 
Should  the  toll  operator  plug  into  the  trunk  jack  before  the  trunk 
operator  plugs  into  the  subscriber's  multiple  jack  or  vice  versa,  the 
disconnect  lamp  associated  with  the  trunk  at  the  local  end  will  light, 
but  will  be  extinguished  again  as  soon  as  both  operators  have  com- 
pleted the  connection. 

When  the  subscribers  have  completed  their  conversation,  the  dis- 
connect signal  from  the  toll  line  will  be  received  in  the  usual  manner. 
The  local  subscriber,  upon  hanging  up  his  receiver,  will  open  the 
circuit  containing  relay  K.  This  in  turn  will  de -energize  relay  H, 
thus  closing  the  circuit  containing  the  supervisory  lamp  in  the  toll 
cord  circuit.  Upon  obtaining  the  double  disconnect  signal  the  line 
operator  will  take  down  the  connections.  This  will  open  the  circuit 
containing  relay  M,  previously  traced,  and  the  release  of  this  relay 
will  light  the  disconnect  lamp  in  the  trunk  circuit.  The  trunk  operator 
will  thereupon  take  down  the  connections. 

(b)  Local-to-Toll  Connection.  —  A  conventional  diagram  of  the  cir- 
cuits used  in  putting  up  a  local-to-toll  connection  with  this  system  is 
shown  in  Fig.  59.  In  the  operation  the  local  operator,  upon  receiving 
a  request  for  a  toll  connection,  will  insert  the  calling  plug  of  the  pair 
used  to  answer  the  call  in  the  multiple  jack  of  an  idle  recording  trunk. 
This  will  light  the  lamp  associated  with  the  trunk  at  the  recording 
operator's  position,  due  to  the  operation  of  relay  H  which  is  bridged 
across  the  tip  and  ring  strands  of  the  circuit.  The  supervisory  lamp 
in  the  local  cord  circuit  will  not  light,  however,  due  to  the  actuation 
of  relay  F,  through  the  coil  of  which  current  is  supplied  to  the  bridged 
relays  of  the  trunk  circuit;  from  the  latter  point  the  circuit  can  be 
followed  to  the  ground  on  retardation  coil  N.  It  will  be  observed  that 
relay  L  is  also  bridged  across  the  trunk  circuit.  This  relay  will  not 
operate,  however,  when  in  parallel  with  relay  H,  because  of  the 


MULTIPLE-LAMP  TOLL  SWITCHBOARDS 


135 


136  TOLL  TELEPHONE  PRACTICE 

) 
relatively  low  resistance  of  the  latter  and  the  high  resistance  of  the 

former.  The  lighting  of  the  lamps  at  the  recording  positions  will 
attract  the  attention  of  the  operators,  as  these  trunks  are  multipled 
at  all  recording  positions,  and  any  operator  can  answer  the  call. 

The  recording  operator  who  answers  will  insert  the  answering  plug 
of  one  of  the  cord  circuits  in  the  recording  trunk  jack.  This  will  close 
the  make  "con  tact  in  the  jack,  which  in  turn  will  close  a  local  circuit 
containing  relays  M  and  K\  the  operation  of  armature  i  of  the  latter 
relay  will  open  the  circuit  containing  the  recording  lamp  and  ex- 
tinguish it.  The  attraction  of  armature  2  of  this  relay  will  close  a 
circuit  that  may  be  traced  from  the  ground  on  the  make  contact  of 
relay  H  to  its  armature,  then  to  the  coil  of  relay  J,  armature  2, 
the  make  contact  and  the  coil  of  relay  K  to  battery.  Thus  relay  / 
will  be  operated  and  will  open  the  bridge  circuit  containing  relay  H\ 
it  will  also  close  a  circuit  that  can  be  traced  from  ground  to  the  make 
contact  and  the  coil  of  this  relay,  to  the  armature  and  the  make 
contact  of  relay  K,  and  thence  through  the  coil  of  the  latter  to  battery. 
Thus  the  ground  on  the  make  contact  of  relay  H,  which  was  originally 
necessary  to  operate  relay  /,  is  finally  replaced  by  the  ground  on  the 
armature  of  the  latter.  The  closing  of  the  circuit  by  means  of  the 
ground  on  the  armature  of  relay  J  will  lock  this  relay  and  also  relay  K. 
The  insertion  of  the  recording  plug  into  the  trunk  jack  will  operate 
relay  Q,  which  is  bridged  across  the  cord  circuit;  this  will  cause  the 
lighting  of  the  "  hold  lamp  "  in  the  recording  cord  circuit.  Since  the 
low-resistance  bridge  containing  relay  Q  replaces  the  low-resistance 
bridge  that  was  opened  by  the  operation  of  relay  /,  it  follows  that 
relay  L  will  not  receive  the  required  operating  current ;  but  at  the  same 
time  sufficient  current  will  flow  through  relay  F  in  the  subscriber's 
cord  circuit  to  hold  it  in  the  closed  position  and  thus  prevent  the 
lighting  of  the  supervisory  lamp  in  this  circuit. 

Only  one-half  of  the  recording  cord  circuit  has  been  shown  on  the 
drawing;  the  other  half  is  shown  in  Fig.  60  and  is  identical  with  Fig.  59, 
with  the  exception  that  no  listening  or  tone-test  keys  are  provided. 
The  recording  operator  is  now  in  a  position  to  converse  with  the  local 
subscriber  and  she  will  consequently  obtain  the  information  necessary 
to  fill  out  the  required  toll  ticket.  Then  in  case  the  recording  operator 
has  good  reason  to  believe  that  it  will  take  some  time  to  complete  the 
connection,  she  will  tell  the  local  subscriber  to  hang  up  his  receiver  and 
that  he  will  be  called  when  his  connection  is  ready. 


MULTIPLE-LAMP  TOLL  SWITCHBOARDS  137 

The  recording  operator  will  then  remove  the  plug  from  the  recording 
trunk  jack,  which  will  extinguish  the  "  hold  lamp."  This  act  will 
also  open  the  make  contact  in  the  jack,  and  disconnect  the  ground 
from  the  circuit  containing  relays  M  and  K  in  series.  Relay  M  will 
thus  be  released,  but  relay  K  is  included  in  the  locking  circuit  con- 
taining relay  /  and  will  thus  remain  closed.  The  withdrawal  of  the 
recording  plug  also  removes  the  low-resistance  circuit  containing  relay 
Q,  which  acted  as  a  shunt  to  the  bridged  circuit  containing  the  high- 
resistance  relay  L\  hence  the  latter  will  now  receive  sufficient  current 
for  its  actuation.  The  operation  of  this  relay  will  close  a  circuit 
through  the  armature  and  break  contact  of  relay  M  and  the  make 
contact  and  armature  of  relay  L,  which  will  short-circuit  the  winding 
of  relay  K.  The  latter  will  consequently  be  released,  whereas  relay 
/  will  remain  locked  until  the  subsequent  release  of  relay  L.  Further- 
more, as  the  circuit  containing  the  high- wound  relay  L  is  now  the  only 
bridge  across  the  trunk  circuit,  relay  F  in  the  cord  circuit  will  not 
receive  sufficient  current  to  hold  up  its  armature;  it  will  therefore  drop 
back  to  normal  and  light  the  disconnect  lamp  in  the  local  operator's 
cord  circuit.  Then,  since  the  local  subscriber  has  been  instructed  to 
hang  up  his  receiver,  the  other  disconnect  lamp  in  the  cord  circuit  will 
also  be  lighted,  and  the  local  operator  upon  receiving  these  double 
disconnect  signals  will  take  down  the  connections.  This  act  will 
release  relay  L  and  open  the  locking  circuit  containing  relay  /,  thus 
restoring  all  the  apparatus  to  its  normal  condition. 

The  recording  operator  will  then  pass  the  toll  ticket  to  the  line 
operator,  who  will  proceed  to  obtain  the 'subscriber  desired  and  com- 
plete the  connection  in  the  same  manner  as  that  just  outlined  in  the 
description  of  the  toll-to-local  connection  shown  in  Fig.  58. 

However,  if  the  recording  operator  has  reason  to  believe  that  the 
connection  can  be  completed  at  once,  she  will  hold  the  local  subscriber 
on  the  line  and  put  a  tone  test  back  over  the  recording  trunk,  by 
operating  the  tone- test  key  in  the  cord  circuit.  This  will  not  give 
a  disconnect  signal  at  the  local  operator's  cord  circuit,  because  the 
resistance  of  the  secondary  winding  of  the  tone-test  transformer  is  low 
enough  to  allow  sufficient  current  to  flow  through  the  winding  of 
relay  F  and  thus  prevent  the  lighting  of  the  disconnect  lamp.  The 
circuit  through  the  secondary  of  the  tone-test  transformer  will  also 
act  as  a  shunt  around  the  high-wound  relay  L  in  the  trunk  circuit  and 
thus  prevent  its  operation. 


138  TOLL  TELEPHONE  PRACTICE 

The  recording  operator  will  next  place  herself  in  communication 
with  the  local  trunk  operator,  giving  the  latter  the  number  of  the  local 
subscriber  desired;  at  the  same  time  she  will  give  the  designation 
"  tone,"  which  denotes  that  the  trunk  operator  will  find  a  tone  on  the 
multiple  jack  of  the  local  line.  The  trunk  operator  then  selects  the 
trunk  to  be  used,  tests  the  multiple  jack  of  the  local  line  and  receives 
the  tone  test.  This  will  inform  her  that  the  line  tested  is  the  one 
desired  and  she  will  therefore  insert  the  plug.  The  recording  operator, 
upon  receiving  the  trunk  assignment,  will  insert  the  calling  plug  of 
the  pair  used  to  answer  the  call  in  the  assigned  multiple  trunk  jack. 
She  will  next  remove  the  answering  plug  from  the  recording  trunk  jack, 
thereby  lighting  the  calling  supervisory  lamp  in  the  local  operator's 
cord  circuit,  as  explained;  the  latter  will  then  take  down  the  connections 
and  thereby  restore  all  the  apparatus  in  the  recording  trunk  circuit  to 
its  normal  state. 

A  diagram  of  the  connection  as  it  now  stands  is  shown  in  Fig.  60 
from  which  it  will  be  seen  that  the  recording  operator  is  connected 
direct  to  the  local  subscriber's  line  by  means  of  the  calling  end  of  the 
recording  cord  and  the  incoming  toll  trunk  circuit.  The  recording 
operator  will  now  send  the  toll  ticket  to  the  proper  line  operator,  who 
will  plug  into  the  multiple  jack  of  the  assigned  trunk  and  hold  the  same 
until  the  connection  is  ready.  As  soon  as  the  line  operator  plugs  into 
the  assigned  trunk,  she  will  close  the  local  make  contact  in  this  jack 
and  thereby  complete  a  circuit  from  ground  by  way  of  the  sleeve 
strand  of  the  trunk  and  cord,  through  the  winding  of  relay  P'  to 
battery.  The  operation  of  this  relay  will  cut  off  the  bridged  super- 
visory relay  Q'  and  light  the  disconnect  lamp  associated  with  the 
recording  cord.  The  recording  operator,  upon  seeing  this  disconnect 
signal,  will  take  down  the  .connection.  The  toll  operator  will  then 
handle  the  call  in  the  manner  previously  described  for  a  toll-to-local 
connection. 

United  States  Telephone  Company's  Equipment 

(a)  Toll-to-Local  Connection.  —  The  discussion  of  the  third  and 
last  trunking  system  used  with  the  multiple -lamp  toll  board  will  now 
be  taken  up.  This  system  contains  a  distinctly  unique  feature  which 
is  not  used  in  either  of  the  other  systems.  It  will  be  observed  by 
referring  to  Fig.  61,  which  shows  the  conventional  circuit  of  a  toll-to- 
local  connection,  that  the  local  trunk  operator  is  equipped  with  a 


MULTIPLE-LAMP  TOLL  SWITCHBOARDS 


140  TOLL  TELEPHONE  PRACTICE 

ringing  lamp  as  well  as  a  disconnect  lamp.  The  trunk  circuit  is 
equipped  for  through  ringing,  however,  and  this  ringing  lamp  merely 
serves  to  indicate  to  the  trunk  operator  whether  or  not  the  line  operator 
has  succeeded  in  obtaining  a  response  from  the  local  subscriber.  When 
the  line  operator  disconnects  and  the  local  subscriber  hangs  up  his 
receiver,  the  trunk  operator 'will  receive  a  double  disconnect  signal  in 
place  of  the  single  signal  in  the  previous  systems.  The  use  of  this 
double  disconnect  signal  seems  hardly  necessary,  inasmuch  as  the  toll 
operator  has  absolute  control  of  the  connection  and  therefore  the 
signal  which  she  gives  is  controlling  and  sufficient. 

The  system  that  is  next  described  in  connection  with  Figs.  61  and 
62,  is  used  by  the  United  States  Telephone  Company  in  its  toll  board 
at  Cleveland,  Ohio,  in  conjunction  with  a  Kellogg  Switchboard  and 
Supply  Company's  two-wire  local  board. 

In  handling  an  incoming  toll  call  the  line  operator  will  place  herself 
in  communication  with  the  local  trunk  operator  by  means  of  an  order 
circuit,  informing  her  of  the  local  number  desired.  The  trunk  operator 
will  then  test  the  multiple  jack  of  the  local  line;  if  it  is  not  busy  she 
will  insert  the  plug  of  one  of  the  trunk  circuits  into  the  jack,  and  at 
the  same  time  give  the  line  operator  the  assignment.  The  act  of 
plugging  into  the  jack  causes  several  operations,  which  will  be  taken 
up  in  the  order  in  which  they  occur.  In  the  first  place,  it  will  be  found 
that  a  circuit  has  been  completed  from  the  ground  at  the  cut-off  relay 
in  the  subscriber's  line,  by  way  of  the  ring  strand  of  the  jack  and  the 
trunk,  through  the  coil  of  relay  A  to  battery.  This  will  cause  the 
actuation  of  the  cut-off  relay  and  also  relay  A .  Armature  i  of  relay 
A  will  close  the  tip  strand  of  the  trunk  and  thereby  remove  the  busy 
test  connection,  while  armature  2  will  complete  a  circuit  which  may  be 
traced  from  ground  by  way  of  the  make  contact  of  the  armature  of 
relay  B  and  thence  through  the  break  contact  of  this  relay  to  the 
ringing  lamp  and  battery,  causing  the  lamp  to  be  lighted.  However, 
the  attraction  of  armature  2  of  relay  A  has  also  completed  a  circuit 
which  can  be  traced  to  the  armature  of  relay  B  and  then  by  way  of  the 
break  contact  of  this  relay,  through  the  coil  of  relay  C  to  battery. 
This  will  cause  the  actuation  of  relay  C. 

It  is  now  essential  to  take  into  consideration  the  condition  of  the 
toll  end  of  the  circuit  in  order  to  understand  the  functions  of  relay  C. 
In  case  the  local  trunk  operator  completes  the  connection  before  the 
line  operator  does  so,  it  will  be  found  that  the  disconnect  lamp  at  the 


MULTIPLE-LAMP  TOLL  SWITCHBOARDS 


141 


142  TOLL  TELEPHONE  PRACTICE 

trunk  position  will  be  lighted,  as  next  explained.  Returning  to  relay 
A  we  can  trace  a  circuit  from  the  ground  on  armature  2  to  the  arma- 
ture of  relay  B,  then  by  way  of  the  break  contact  of  this  relay  to  the 
break  contact  of  relay  D  and  thence  by  way  of  the  armature  and  the 
disconnect  lamp  to  battery.  However,  in  case  the  toll  operator  has 
previously  inserted  the  plug  in  the  trunk  jack,  the  conditions  are 
materially  changed;  in  this  case  a  circuit  has  been  completed  from  the 
ground  on  armature  3  of  relay  C,  to  winding  i  of  the  repeating  coil, 
over  the  tip  strands  of  the  trunk  and  the  toll  cord  circuit,  through 
winding  2  of  relay  F,  thence  by  way  of  the  ring  strand  of  the  cord  and 
the  trunk  circuit,  through  winding  2  of  the  repeating  coil  to  armature 
4  of  relay  C,  then  by  way  of  the  make  contact  of  this  relay  through 
relay  D  and  finally  to  battery.  The  completion  of  the  circuit  just 
outlined  will  cause  the  actuation  of  relays  F  and  D;  relay  F  will  light 
the  lamp  in  the  toll  cord  circuit  and  relay  D  will  open  the  circuit 
containing  the  disconnect  lamp.  This  will  inform  the  trunk  operator 
that  the  toll  end  of  the  connection  has  been  properly  completed.  It 
will  be  clear  from  the  foregoing  that  in  case  the  toll  operator  completes 
her  end  of  the  connection  prior  to  the  completion  of  the  local  end,  the 
ringing  lamp  will  be  the  only  one  to  light  in  the  trunk  circuit;  should 
the  connections  be  put  up  in  the  reverse  order,  both  the  ringing  and 
the  disconnect  lamps  will  light,  the  latter  being  extinguished  when  the 
toll  operator  completes  her  end  of  the  connection.  The  connection 
has  now  been  traced  to  the  stage  where  the  toll  operator  is  ready  to 
ring  the  local  subscriber. 

It  will  be  evident  that  whenever  the  toll  operator  actuates  the  ringing 
key,  relay  E  will  be  energized  and  will  complete  a  circuit  which  can  be 
traced  from  the  ground  on  the  make  contact  of  this  relay,  by  way  of 
its  armature  to  the  coil  of  relay  G  and  thence  to  battery.  Thereupon 
relay  G  will  be  energized  and  the  operation  of  its  armatures  will  fulfill 
the  functions  of  a  local  ringing  key  at  the  trunk  position.  In  case  the 
local  switchboard  is  equipped  with  selective  ringing  for  party-line 
service,  each  trunk  circuit  is  provided  with  a  master  key,  as  shown  in 
the  American  Telephone  and  Telegraph  Company's  circuit  in  Fig.  56. 
The  trunk  operator  is  called  upon  to  help  in  the  operation  of  ringing 
only  when  a  party-line  subscriber  is  desired;  and  even  in  that  case,  the 
operation  consists  merely  of  depressing  the  master  key. 

When  the  subscriber  answers,  relay  B  in  the  trunk  circuit  will  be 
energized,  due  to  the  completion  of  the  following  circuit;  from  the 


MULTIPLE-LAMP  TOLL   SWITCHBOARDS  143 

ground  on  the  coil  of  relay  B,  through  the  make  contact  and  armature 
i  of  relay  A,  to  the  tip  of  the  cord  and  plug,  thence  over  the  tip  strand 
of  the  line  circuit,  through  the  subscriber's  set,  returning  over  the 
ring  strand  of  the  line  and  the  trunk  circuit  and  through  relay  A  to 
battery. 

Relay  B  performs  several  operations.  In  the  first  place,  it  opens 
the  ground  connection  in  the  circuit  containing  the  ringing  lamp, 
thereby  extinguishing  the  lamp  and  informing  the  trunk  operator  that 
the  subscriber  has  answered.  Secondly,  it  will  disconnect  the  ground 
from  the  circuit  containing  relay  C  and  therefore  this  relay  will  release. 
The  last  operation  will  open  the  circuit  that  has  previously  been  traced 
through  the  toll  cord  circuit.  Thus  relay  F  will  release  and  thereby 
extinguish  the  supervisory  lamp,  which  will  inform  the  toll  operator 
that  her  subscriber  has  answered.  The  release  of  relay  C  will  also 
cause  the  release  of  relay  D,  in  preparation  for  the  subsequent  receipt 
of  a  disconnect  signal.  This  now  concludes  the  operation,  up  to  the 
point  of  commencing  conversation  over  the  toll  line. 

When  the  conversation  is  finished,  the  local  subscriber  will  hang  up 
his  receiver  and  a  disconnect  signal  should  be  received  from  a  distant 
toll  operator.  The  latter  will  light  the  supervisory  lamp  in  the  toll 
cord  circuit  as  explained  in  the  description  of  the  toll-to-toll  connection. 
The  act  of  hanging  up  the  receiver  at  the  local  station  will  release  relay 
B  in  the  trunk  circuit  and  complete  the  ground  connection  for  the 
circuit  containing  the  ringing  lamp  and  the  circuit  containing  relay  C. 
The  actuation  of  relay  C  will  complete  the  circuit  through  relay  F  in 
the  toll  cord  circuit  and  thus  the  second  supervisory  lamp  will  be 
lighted.  However,  the  disconnect  lamp  in  the  trunk  circuit  will  not 
light,  since  the  circuit  which  energized  relay  F  also  contains  relay  D 
and  the  latter  will  open  the  circuit  containing  the  disconnect  lamp. 
When  the  toll  operator  receives  the  disconnect  signals  mentioned,  she 
will  remove  the  connections.  This  will  open  the  circuit  through  relay 
D  and  the  latter  will  close  the  disconnect  lamp  circuit  at  the  local 
board.  The  trunk  operator  now  has  a  disconnect  signal  from  each 
end  of  the  circuit  and  will  therefore  take  down  the  connections,  which 
will  release  relay  A  and  restore  the  apparatus  to  its  normal  condition. 

(b)  Local-to-Toll  Connection.  —  The  recording  trunk  circuit  used 
by  the  United  States  Telephone  Company  differs  from  the  previous 
systems  in  the  respect  that  no  provision  is  made  for  holding  the  local 
subscriber  while  the  connection  is  being  established.  In  this  system 


144 


TOLL  TELEPHONE  PRACTICE 


all  trunk  assignments  are  obtained  by  the  line  operator  and  the  work 
of  the  recording  operator  is  confined  entirely  to  noting  the  details  of 
the  call  on  the  ticket.  The  recording  circuit  is  shown  in  Fig.  62.  The 
trunk  jacks  at  the  local  switchboard  are  multipled  in  each  section. 
When  the  local  operator  receives  a  request  for  a  toll  connection,  she 
inserts  the  calling  plug  in  the  jack  of  an  idle  trunk  and  rings  the  re- 
cording operator.  This  will  light  the  calling  supervisory  lamp  at  the 
recording  board,  which  remains  lighted  until  the  recording  operator 
answers.  Thus  the  work  of  the  local  operator  in  handling  a  recording 

I 

SUBS.  SW.  BD 


FIG.  62.  —  Toll  Recording  Circuit,  Used  by  the  United  States  Telephone  Company  at 

Cleveland,  Ohio. 

connection  is  the  same  as  that  required  in  a  local  connection.  The 
local  operator,  by  ringing  on  the  recording  trunk,  will  energize  winding 
i  of  relay  A .  This  will  lock  the  armature  by  means  of  a  circuit  which 
can  be  traced  from  battery,  through  winding  2,  via  the  armature  and 
make  contact  of  relay  A ,  to  the  break  contact  and  armature  of  relay 
B  and  then  to  ground.  The  operation  of  relay  A  will  light  the  record- 
ing trunk  lamps  at  the  recording  positions  and  the  call  will  be  answered 
by  any  of  the  operators.  The  insertion  of  the  plug  of  one  of  the 
recording  cords  will  complete  a  circuit  from  the  battery  connection 
on  the  sleeve  conductor  of  the  cord,  through  the  winding  of  relay  B 
to  ground.  Relay  B  will  operate  and  open  the  locking  circuit  of  relay 
A,  thus  extinguishing  the  recording  lamps.  When  the  recording 
operator  has  obtained  the  desired  information,  she  will  instruct  the 
subscriber  to  hang  up  his  receiver  and  wait  until  he  is  called.  She 


MULTIPLE-LAMP  TOLL  SWITCHBOARDS  145 

will  then  remove  the  connection,  thereby  restoring  the  trunk  apparatus 
to  its  normal  state  and  at  the  same  time  lighting  the  calling  supervisory 
lamp  in  the  local  cord  circuit.  The  subscriber,  upon  hanging  up  his 
receiver,  will  light  the  answering  disconnect  lamp,  thus  giving  the  local 
operator  the  complete  disconnect  signal.  The  ticket  made  out  by 
the  recording  operator  is  passed  to  the  proper  line  operator,  who  will 
proceed  as  described  for  the  toll- to-local  connection. 

Auxiliary  Toll  Board  Circuits.  —  In  connection  with  the  multiple- 
lamp  toll  board,  it  seems  advisable  to  describe  a  type  of  interposition 
trunk  and  a  messenger  circuit  sometimes  used  with  this  equipment. 
A  detailed  description  will  also  be  given  of  the  method  of  cabling  and 
the  general  scheme  of  cross-connection  at  the  distributing  frames. 

The  purpose  and  advantages  of  an  interposition  trunk  have  been 
fully  described  in  Chapter  VII  in  connection  with  the  magneto- 
multiple  board.  The  trunk  of  this  type  shown  in  Fig.  63  will  there- 
fore be  described  with  reference  only  to  the  method  of  operation. 
In  order  to  make  the  narrative  as  simple  as  possible,  only  one-half  of 
a  toll  operator's  cord  circuit  is  shown  at  each  end  of  the  trunk.  The 
trunk  jacks  at  the  calling  end  are  multipled  in  each  section  of  the 
board,  while  the  jack  at  the  answering  end  is  located  at  some  particular 
section. 

Whenever  an  operator  desires  to  communicate  with  some  other  oper- 
ator in  the  office,  she  will  plug  into  the  multiple  jack  which  is  numbered 
to  correspond  with  the  position  at  which  the  trunk  terminates.  The 
act  of  plugging  into  the  jack  causes  several  operations,  which  will  be 
described  in  the  order  of  occurrence.  In  the  first  place,  the  busy 
lamps  associated  with  the  multiple  jacks  will  all  be  lighted,  due  to  the 
fact  that  the  plug  closes  the  make  contact  at  the  jack.  This  contact 
closes  a  circuit  from  the  ground  on  the  make  spring  in  the  jack,  through 
all  the  busy  lamps  (in  parallel)  to  battery.  This  guards  the  trunk 
while  in  use.  In  the  second  place,  a  circuit  is  completed  from  battery, 
by  way  of  the  coil  2  of  relay  B,  to  the  break  contact  and  armature  i 
of  relay  A ,  to  the  ring  strand  of  the  trunk  circuit  and  thence  by  way 
of  the  ring  strand  of  the  calling  operator's  cord  circuit,  through  winding 
i  of  relay  Df,  to  the  tip  strand  of  the  cord  circuit,  over  the  tip  strand 
of  the  trunk,  to  armature  3  of  the  break  contact  of  relay  A,  through 
winding  i  of  relay  B  and  then  to  ground.  The  completion  of  the  above 
circuit  will  energize  relays  B  and  Df.  Relay  Df  will  light  the  calling 
operator's  supervisory  lamp  in  the  usual  manner.  Relay  B  will  com- 


146 


TOLL  TELEPHONE  PRACTICE 


MULTIPLE-LAMP  TOLL  SWITCHBOARDS  147 

plete  the  answering  lamp  circuit/  which  can  be  traced  as  follows:  from 
ground,  by  way  of  the  make  contact  and  armature  of  relay  B,  to 
the  armature  and  break  contact  of  relay  C  and  thence  through  the 
answering  lamp  and  the  pilot  relay  to  battery.  This  lamp  will  signal 
the  called  operator  to  answer.  The  act  of  plugging  into  the  answering 
jack  will  complete  a  circuit  from  battery  through  the  coil  of  relay  E, 
over  the  sleeve  strand  of  the  cord  circuit,  to  the  sleeve  of  the  trunk 
jack,  thence  by  way  of  the  coil  of  relay  A ,  to  the  make  contact  of  the 
multiple  trunk  jack  and  then  to  ground.  Thus  relays  A  and  E  will 
be  energized.  The  actuation  of  relay  A  will  open  the  circuit  containing 
winding  i  of  relay  Df,  due  to  the  operation  of  the  break  contacts  at 
armatures  i  and  3.  Therefore  relay  B  will  release  and  open  the  line 
lamp  circuit;  relay  D'  will  also  release  and  extinguish  the  supervisory 
lamp  in  the  calling  operator's  cord  circuit,  thereby  informing  her  that 
the  other  operator  has  answered.  The  calling  operator  thereupon 
actuates  her  listening  key  and  is  thus  in  a  position  to  converse  with 
the  operator  called.  Armature  2  of  relay  A  completes  another  circuit 
which  can  be  traced  as  follows :  from  the  ground  on  the  make  contact 
of  the  trunk  multiple  jack,  to  the  make  contact  and  the  armature  2 
of  relay  A,  through  the  winding  of  relay  C  and  thence  to  battery. 
Thus  relay  C  will  be  energized  and  armature  i  will  lock  the  relay,  until 
the  calling  operator  withdraws  the  plug,  by  means  of  a  circuit  that  can 
be  traced  from  battery  through  the  winding  to  armature  i  and  the 
make  contact,  thence  to  the  make  contact  in  the  trunk  multiple  jack 
and  from  there  to  ground.  After  the  operators  have  completed  their 
conversation,  they  will  withdraw  the  plugs.  When  the  answering 
operator  disconnects,  the  circuit  containing  relay  A  will  be  opened 
and  the  relay  will  release,  thus  completing  again  the  circuit  through 
the  coils  of  relay  B  in  the  trunk  circuit  and  relay  D  in  the  calling 
operator's  cord  circuit,  which  will  light  the  supervisory  lamp.  The 
trunk  line  lamp  will  not  relight,  however,  due  to  the  fact  that  relay 
C  is  locked.  When  the  calling  operator  disconnects,  however,  the  jack 
contact  is  thereby  opened  and  relay  C  is  released;  at  the  same  time  the 
circuit  containing  relay  B  is  opened,  thus  restoring  the  apparatus  to 
its  normal  condition. 

For  the  convenience  of  the  operator  located  at  the  toll  board  and 
for  the  purpose  of  distributing  the  toll  tickets,  each  section  at  the  toll 
board  is  equipped  with  a  messenger  key.  The  purpose  of  this  key, 
as  the  name  implies,  is  to  call  messengers.  These  messengers  carry 


148  TOLL  TELEPHONE  PRACTICE 

telephone  directories  and  any  other  essential  material  from  one  oper- 
ator to  another,  and  also  distribute  the  toll  tickets,  at  the  direction 
of  the  recording  operators,  among  the  proper  line  operators. 

The  operation  of  the  messenger  circuit  is  as  follows :  Whenever  any 
operator  desires  to  call  a  messenger,  she  actuates  the  messenger  key, 
located  in  the  lock  rail;  this  closes  a  circuit  containing  a  lamp  situated 
in  an  annunciator,  that  is  located  in  a  conspicuous  part  of  the  operating 
room.  The  closing  of  this  circuit  will  light  the  lamp  and  thus  display 
the  position  number  of  the  operator  requiring  messenger  service. 
This  will  attract  the  attention  of  a  messenger,  who  will  respond  to  the 
call.  As  soon  as  the  messenger  reaches  the  operator  signaling,  the 
messenger  will  restore  the  key  to  normal  and  thus  extinguish  the  lamp. 
Messenger  service  as  outlined  above  is  used  in  all  toll  offices,  except 
some  of  the  very  large  offices  of  the  American  Telephone  and  Tele- 
graph Company.  In  these  latter  exchanges  a  system  of  tubes  is  in- 
stalled by  means  of  which  the  tickets  are  distributed  pneumatically. 

In  this  instance,  each  section  of  the  toll  board  is  provided  with  tubes 
to  receive  and  deliver  tickets.  All  tickets  that  are  to  be  delivered 
to  the  various  line  operators  for  completing  connections  are  first 
delivered  to  the  ticket  distributing  operators,  through  the  tubes  leading 
from  the  recording  board.  The  distributing  operators  in  turn  send 
the  tickets  to  the  proper  line  operators  by  means  of  tubes  to  the  line 
positions.  The  distributing  position  forms  a  general  clearing  house 
for  all  tickets.  These  tubes  are  rectangular  in  shape,  with  an  opening 
of  about  one-eighth  of  an  inch  and  a  width  equal  to  that  of  the  toll 
ticket.  All  joints  in  these  tubes  must  be  carefully  made  so  as  to  avoid 
any  catching  or  tearing  of  tickets  and  sharp  turns  are  to  be  guarded 
against.  Each  ticket  is  folded  back  at  one  end  so  as  to  be  caught  by 
the  air  suction  in  the  tube  and  carried  to  its  destination.  These  tubes 
are  stacked  in  a  manner  similar  to  multiple  cables,  in  a  runway  which 
ordinarily  extends  over  the  top  of  the  switchboard  sections.  The 
accompanying  illustration,  in  Fig.  64,  clearly  shows  the  ticket  tube 
runway  and  the  ticket  distributing  board.  This  board  is  located 
centrally  between  the  two  lines  of  toll  sections  and  is  elevated  to  a 
height  about  equal  to  the  top  of  the  toll  board.  The  ticket  receiving 
and  sending  boxes,  at  the  various  line  positions,  are  mounted  in  the 
middle  panel  of  each  toll  section. 

Wiring  of  a  Toll-line  Terminal.  —  The  method  of  cabling  and  the 
distribution  of  apparatus  about  to  be  explained  is  shown  in  Fig.  65; 


MULTIPLE-LAMP  TOLL  SWITCHBOARDS 


149 


TOLL  TELEPHONE  PRACTICE 


rrn    rrn  rrn 


" 


MULTIPLE-LAMP  TOLL  SWITCHBOARDS  151 

it  is  applicable  to  any  system  that  has  been  described  and  is  the 
standard  method  of  wiring  a  toll-line  terminal.  It  is  also  standard 
practice  in  wiring  toll  switchboards  to  use  talking  conductors  as  large 
at  least  as  No.  19  B.  &  S.  gauge,  while  the  signaling  conductors  are 
usually  No.  22  or  No.  24  B.  &  S.  gauge;  No.  22  is  preferable  for 
mechanical  reasons. 

It  will  be  noted  by  referring  to  the  figure  that  the  toll  line,  upon 
entering  the  office,  is  carried  first  to  the  high-current  arresters  on  the 
main  distributing  frame.  The  protection  at  this  point  consists  of  line 
fuses  and  carbon  block  lightning  arresters  similar  to  those  shown  in 
Fig.  66.  The  toll  line  is  then  cross-connected  to  the  switchboard  side 


FIG.  66.  —  High  Potential  and  Abnormal  Current  Arresters. 

of  the  frame  and  from  there  carried  to  the  test  panel.  The  uses  of 
this  panel  will  be  touched  upon  but  briefly  at  present,  as  a  full  explana- 
tion will  be  given  in  a  subsequent  chapter.  It  will  be  noted  that  each 
line  entering  the  office  is  associated  at  the  panel  with  six  spring  jacks, 
three  for  each  side  of  the  line.  These  jacks  are  grouped  in  pairs  and 
a  suitable  twin  plug  is  furnished  with  the  cord  circuits  at  the  panel. 
The  object  of  employing  three  pairs  of  jacks  is  as  follows.  In  case  a 
plug  is  inserted  in  jacks  3  and  6,  the  switchboard  end  of  the  line  circuit 
is  cut  off  by  means  of  the  break  contacts  in  the  jacks  and  the  cord 
circuit  is  connected  directly  to  the  outgoing  line.  If  the  plug  is  in- 


152  TOLL  TELEPHONE  PRACTICE 

serted  in  jacks  2  and  5  a  similar  condition  exists,  with  the  exception 
that  the  busy  signals  associated  with  the  line  at  the  toll  board  are  now 
displayed.  The  circuit  containing  the  busy  signal  is  completed  by 
means  of  the  make  contact  in  jack  5.  When  a  plug  is  inserted  in 
this  jack,  a  circuit  can  be  traced  from  battery  through  the  jack  contact 
to  the  intermediate  distributing  frame  and  thence  by  way  of  the  jumper 
through  the  cut-off  relay  A  to  ground.  Thus  the  cut-off  relay  is 
energized  and  the  busy  lamp  is  lighted,  as  explained  in  connection 
with  Fig.  53.  In  case  the  plug  is  inserted  in  jacks  i  and  4,  it  will  be 
noted  that  the  line  side  of  the  circuit  is  cut  off  and  the  switchboard 
side  is  connected  direct  to  the  cord  circuit.  The  object  of  these 
arrangements  will  be  fully  explained  later;  jack  pair  i  and  4  and  pair 
3  and  6  are  used  for  compositing  and  simplexing,  while  2  and  5  are 
used  by  the  wire  chief  for  testing  the  toll  line  and  i  and  4  for  testing 
the  office. 

Having  traced  the  line  to  the  test  panel,  we  find  that  it  is  next 
carried  to  the  intermediate  distributing  frame.  The  cable  carrying 
the  lines  over  is  usually  a  33-  or  a  63-wire  cable,  as  lines  are  usually 
grouped  for  convenience  in  units  of  ten  or  multiples  thereof;  the  three 
spare  conductors  are  for  emergency  use.  The  distributing  frame  end 
of  the  cable  terminates  in  a  three-point  terminal  block  and  is  cross- 
connected  to  the  multiple  terminal  strip  on  the  switchboard  side  of 
the  frame. 

It  will  be  noted  that  the  answering  side,  as  well  as  the  multiple  side, 
of  the  line  circuit  terminates  at  the  distributing  frame  in  six-point 
terminal  strips.  The  method  of  cabling  to  these  strips  is  as  follows. 
The  tip  and  the  ring  springs  of  the  answering  jacks  are  connected  to 
clips  2  and  3  of  the  answering  terminal  strip  by  means  of  a  pair  of 
No.  19  B.  &  S.  wire  carried  in  the  "  intermediate  to  answering  " 
cable.  Terminal  clips  i  and  4  receive  the  wires  from  the  busy  lamp 
and  the  sleeve  of  the  answering  jack,  respectively,  and  are  run  as  a 
pair  in  a  separate  cable.  Terminal  clips  5  and  6  connect  with  the 
night  switching  key  by  means  of  a  pair  of  wires  in  a  third  cable.  The 
three  cables  last  mentioned  each  contain  ten  service  pairs  and  one 
spare  pair.  The  cable  which  contains  the  talking  conductors  should 
be  composed  of  No.  19  B.  &  S.,  as  stated  above,  and  the  other  two 
cables  of  No.  22  B.  &  S.  gauge.  Although  it  is  customary  to  install 
sufficient  cable  to  care  for  ten  answering  jack  equipments,  this  by  no 
means  signifies  that  ten  lines  are  to  terminate  at  one  operator's  position. 


MULTIPLE-LAMP  TOLL  SWITCHBOARDS  153 

It  is  customary,  for  various  reasons,  to  furnish  equipment  in  the 
answering  jack  space  for  more  lines  than  ordinarily  can  be  handled 
by  the  operator.  The  principal  reasons  for  this  are,  first,  that  standard 
apparatus  for  the  answering  jack  equipment  is  usually  made  in  strips  of 
ten;  and  second,  should  trouble  develop  in  one  of  the  lines  between  the 
frame  and  the  answering  jack,  a  spare  terminal  can  be  substituted  by 
cross-connecting  at  the  intermediate  frame. 

Having  disposed  of  the  answering  terminal  strip,  attention  will  now 
be  directed  to  the  multiple  terminal.  It  will  be  noted  that  on  this  ter- 
minal clips  2  and  3  are  reserved  for  the  tip  and  the  ring  of  the  mul- 
tiple jack.  In  addition  to  the  pair  of  conductors  leading  to  the 
answering  jack,  there  is  a  pair  which  leads  to  the  heat  coils  at  the 
relay  rack.  These  heat  coils  may  be  located  on  the  relay  rack  itself, 
in  which  case  the  question  of  cabling  is  somewhat  simplified;  or  they 
may  be  located  on  the  main  distributing  frame.  When  located  on 
the  main  frame  they  are  usually,  for  convenience  in  mounting  and 
manufacturing,  made  up  as  standard  sneak  current  and  lightning 
arresters,  like  those  used  in  local  offices.  In  the  latter  case,  it  is 
customary  to  use  dummy  carbons  in  place  of  the  standard  carbons 
and  micas.  These  heat  coils  serve  to  guard  against  sneak  currents 
which  might  get  past  the  fuses  at  the  high-current  arrester  frame  and 
thus  damage  the  relay  equipment. 

Returning  to  the  cabling,  it  will  be  observed  that  clips  i,  4  and  5 
are  also  cabled  to  the  relay  rack;  these  wires  are  carried  in  a  single 
cable  as  one  pair  and  one  single  wire.  There  now  remain  but  three 
wires  on  this  terminal  that  have  not  been  accounted  for,  namely,  one 
to  the  busy  lamp,  one  to  the  sleeve  of  the  multiple  jack  and  one  to 
the  night  line  lamp.  The  first  two  are  wired  in  a  cable  as  one  pair 
and  the  third  is  wired  in  another  cable  as  a  single  conductor;  they  take 
terminals  i,  4  and  6  respectively. 

Having  accounted  for  all  of  the  wires  on  the  terminal  strips  at  the 
frame,  the  next  consideration  is  the  method  of  cross-connecting. 
The  cross  connections  or  "jumpers"  are  indicated  in  the  figure  by 
dotted  lines.  A  toll  circuit  is  similar  to  a  local  subscriber's  circuit 
in  the  respect  that  the  relay  equipment  is  associated  with  the  mul- 
tiple; therefore,  the  wires  from  the  test  panel  are  cross-connected  to 
the  tip,  ring  and  sleeve  clips  of  the  multiple  terminal  strip.  Springs 
i  and  6  of  the  multiple  terminal  strip  are  cross-connected  to  clips  i 
and  6  of  the  answering  strip. 


154  TOLL  TELEPHONE  PRACTICE 

For  the  purpose  of  making  these  connections  more  clearly  under- 
stood, an  incoming  call  will  be  traced  in  detail. 

An  incoming  signal  (alternating  current)  from  the  toll  line  will  take 
the  following  path.  Starting  from  the  high-current  arrester  on  the 
line  side  of  the  main  frame,  it  passes  through  the  jumper  and  the 
terminal  spring,  to  the  make  contacts  of  jacks  3,  i  and  2  respectively 
and  then  to  clip  i  of  the  three-point  terminal.  Thence  it  may  be 
traced  by  means  of  the  jumper  to  clip  2  on  the  multiple  terminal, 
through  the  heat  coil  to  the  make  contact  of  armature  3  of  relay  A ,  to 
coil  i  of  relay  B  and  through  the  other  heat  coil;  it  next  passes  to  clip  3 
of  the  multiple  terminal,  over  the  jumper  wire  to  clip  2  of  the  three- 
point  terminal,  through  the  three  jacks  in  the  test  panel  and  back  to 
the  main  frame.  Consequently  relay  B  will  be  energized  and  per- 
manently locked,  due  to  a  circuit  that  may  be  traced  from  battery 
to  coil  2  of  relay  B,  thence  to  the  make  contact  and  the  armature  of 
the  same  relay,  to  the  break  contact  and  armature  i  of  relay  A  and 
then  to  ground.  This  will  light  the  line  lamp  and  the  busy  lamps. 
The  circuit  containing  the  busy  lamps  can  be  traced  from  the  ground 
on  armature  i  of  relay  A ,  by  way  of  the  break  contact,  to  the  armature 
of  relay  B  and  its  make  contact,  to  the  break  contact  and  armature  2 
of  relay  A  and  thence  to  clip  i  of  the  multiple  terminal.  Commencing 
at  this  point  the  lamps  associated  with  the  multiple  jacks  are  wired 
in  multiple  to  battery;  whereas  the  circuit  for  the  answering  busy 
lamp  can  be  traced  through  the  jumper  connected  to  clip  i  on  the 
answering  terminal  and  thence  through  the  lamp  to  battery. 

The  line  lamp  circuit  can  be  traced  from  battery  through  the  pilot 
relay  and  the  switching  key  to  clip  5  of  the  answering  terminal,  from 
there  through  the  jumper  to  the  same  clip  on  the  multiple  terminal, 
thence  to  the  make  contact  and  the  armature  of  relay  B,  to  the  break 
contact  and  armature  i  of  relay  A  and  finally  to  ground.  In  case  the 
night  switch  is  operated  it  will  be  observed  that  the  circuit  is  shifted 
to  the  make  contact  of  the  switch ;  from  here  it  can  be  traced  to  clip  6 
on  the  answering  terminal,  through  the  jumper  to  the  multiple  ter- 
minal and  through  the  night  line  lamp  to  battery.  When  the  operator 
answers  by  plugging  into  either  the  multiple  jack  or  the  answering 
jack,  it  follows,  since  the  sleeves  of  these  jacks  are  connected  by  the 
jumper  from  clip  4  of  the  multiple  terminal  to  the  same  clip  on  the 
answering  terminal,  that  the  cut-off  relay  A  will  be  operated  and 
the  line  lamp  extinguished.  This  is  due  to  the  fact  that  battery  is 


MULTIPLE-LAMP  TOLL   SWITCHBOARDS  155 

connected  to  the  sleeve  of  the  plug;  and  therefore,  the  act  of  inserting 
the  plug  completes  the  circuit  to  clip  4  and  the  coil  of  relay  A  to  ground. 
The  operation  of  relay  A  disconnects  the  signaling  apparatus  from 
the  line  and  transfers  the  ground  connection  of  the  busy  lamp  circuit 
to  armature  2  of  relay  A,  as  was  explained  in  connection  with  Fig.  53. 


: 


CHAPTER  IX 
TOLL  CONNECTIONS  TO  LOCAL  AUTOMATIC  SYSTEMS 

THE  interconnection  of  toll  lines  with  local  lines  which  terminate 
in  an  automatic  switchboard,  and  vice  versa,  has,  to  a  great  extent, 
complicated  the  toll  switchboard  used  for  this  class  of  service.  This 
complication  arises  from  the  fact  that  means  must  be  provided  whereby 
a  toll  operator  can  complete  a  connection  with  subscribers  connected 
to  the  automatic  system  and  each  such  subscriber  must  be  able  to 
reach  the  toll  board.  The  latter  operation  is  not  especially  compli- 
cated as  all  automatic  telephones  are  now  provided  with  an  extra 
number  on  the  dial,  which,  when  selected,  connects  the  subscriber, 
by  means  of  a  trunk,  direct  to  the  toll  board.  There  are  two  general 
schemes  of  reaching  the  automatic  subscriber  from  the  toll  board;  the 
one  most  generally  used  provides  the  toll  operator  with  a  calling  dial, 
by  means  of  which  she  can  select  the  subscriber  through  the  switches 
in  the  same  manner  that  one  automatic  subscriber  selects  and  calls 
another.  This  scheme,  while  very  satisfactory  for  small  boards,  is 
too  slow  in  operation  for  large  toll  offices. 

The  other  method  referred  to  involves  considerable  extra  expense, 
as  all  the  local  lines  must  be  carried  through  a  switching  panel  before 
they  reach  the  automatic  switches.  At  the  switching  panel  each  line 
passes  through  a  double  cut-off  jack.  This  method  is  used  in  the 
plant  of  the  Citizens'  Telephone  Company,  at  Grand  Rapids,  Michigan. 
Fig.  67  gives  a  view  of  their  toll  operating  room,  which  shows  at  the 
extreme  left  a  switching  panel  similar  to  the  one  referred  to  above. 
The  circuits  of  a  toll  board  in  which  this  scheme  is  used  may  be  of 
any  standard  type.  When  a  call  for  an  automatic  subscriber  is 
received,  the  toll  operator  will  communicate,  over  an  order  circuit, 
with  the  local  switching  operator,  who  will  assign  the  trunk  to  be  used 
and  then  insert  the  trunk  plug  in  the  jack  connected  with  the  line 
called  for.  The  insertion  of  the  plug  in  the  jack  cuts  off  the  auto- 
matic switch  associated  with  the  line  and  renders  it  "  busy  "  to  all 
other  calls.  The*  toll  operator  then  has  a  direct  connection  to  the  line 
called  for. 

156 


TOLL  CONNECTIONS  TO  LOCAL  AUTOMATIC  SYSTEMS         157 


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158  TOLL  TELEPHONE  PRACTICE 

Each  of  the  above  schemes  has  individual  advantages.  The  first 
one  costs  considerably  less  to  install  than  the  second,  but  is  slower  in 
operation.  The  second  method  has  an  additional  advantage  in  the 
respect  that  the  automatic  switches  are  entirely  eliminated  from  the 
connection.  This  last-mentioned  feature  may  seem  of  minor  impor- 
tance, but  the  omission  of  each  additional  contact  and  length  of  cable 
from  the  toll  connection  is  a  distinct  advantage. 

One  of  the  earliest  and  largest  boards  of  the  first  general  type  was 
designed  and  built  by  the  Kellogg  Switchboard  and  Supply  Company 
and  installed  at  Dayton,  Ohio.  Some  idea  of  the  general  arrangement 
of  the  apparatus  can  be  had  by  referring  to  the  accompanying  illustra- 
tion, Fig.  68.  At  the  time  this  board  was  designed  there  was  practi- 
cally no  data  that  would  serve  as  a  guide  in  planning  the  trunk  circuits. 
The  trunks  naturally  constituted  the  all-important  and  novel  feature 
in  this  work  and  this  undertaking  was  therefore  viewed  with  consider- 
able interest.  This  board  has  now  been  in  use  for  a  number  of  years 
and  has  given  good  service.  The  circuits  are  of  sufficient  interest  to 
merit  a  description. 

Fig.  69  shows  a  diagram  of  the  connection  from  a  toll  line  to  an 
automatic  subscriber's  line.  The  toll  end  of  the  connection  is  com- 
pleted in  the  usual  way.  The  line  operator,  upon  receiving  an  inward 
call,  tests  the  outgoing  trunk  multiple  and  inserts  the  calling  plug 
in  the  first  idle  trunk.  This  completes  a  circuit  through  relays  A 
and  B.  The  attraction  of  armature  3  of  relay  B  completes  a  circuit 
through  relay  C,  but  as  these  two  relays  have  no  immediate  effect 
upon  the  operation  they  will  not  be  considered  until  later.  The 
operator  is  now  ready  to  select  the  automatic  subscriber.  This  is 
accomplished  by  the  operation  of  key  i,  which  connects  the  calling 
cord  with  the  automatic  dial.  The  operator  can  now  actuate  the  dial 
and  select  any  subscriber  desired,  in  the  manner  that  one  automatic 
subscriber  selects  another.  When  the  conversation  is  completed  the 
disconnect  signal  from  the  toll  line  is  received  in  the  usual  manner. 
The  automatic  subscriber  upon  placing  his  receiver  on  the  hook 
connects  each  line  conductor  to  ground  momentarily.  This  ground 
connection  can  be  traced  to  battery  through  each  winding  of  relay  F. 
The  subsequent  actuation  of  relay  F  completes  a  circuit  from  the 
ground  on  the  make  contact  and  the  armature  of  this  relay  through 
one  winding  of  relay  E  to  battery.  Relay  E  is  thereby  energized  and 
completes  a  circuit  which  may  be  traced  from  ground  on  the  break 


TOLL  CONNECTIONS  TO  LOCAL  AUTOMATIC  SYSTEMS         159 


i6o 


TOLL  TELEPHONE  PRACTICE 


TOLL  CONNECTIONS  TO  LOCAL  AUTOMATIC  SYSTEMS         161 

contact  of  key  3  to  the  make  contact  and  the  armature  of  relay  E  and 
through  the  other  winding  of  this  relay  to  battery.  This  circuit  holds 
the  relay  in  a  closed  position  until  key  3  is  actuated,  as  relay  F  will 
remain  closed  for  only  a  very  short  interval.  The  operation  of  relay  E 
also  completes  a  circuit  from  .ground  through  the  disconnect  lamp  to 
battery,  thereby  notifying  the  operator  that  the  automatic  subscriber 
has  hung  up  his  receiver.  The  operator  will  then  take  down  the  con- 
nection, which  will  release  relay  B.  Relay  C  is  still  closed,  as  the 
circuit  through  this  relay  is  completed  by  the  ground  connected  to 
the  back  contact  of  relay  D.  As  soon  as  relay  B  releases,  a  ground  is 
placed  on  the  line  conductors  of  the  trunk  circuit  by  way  of  the  arma- 
ture of  relay  C,  through  the  winding  of  relay  D  and  the  back  contacts 
and  the  armatures  i  and  2  of  relay  B.  This  ground  connection  causes 
a  flow  of  current  from  the  automatic  switches,  which  energizes  relay 
D  and  thus  removes  the  ground  connection  from  the  circuit  containing 
relay  C.  The  release  of  relay  C  will  remove  the  ground  from  the  coil 
of  relay  D,  which  will  likewise  release  and  restore  the  trunk  circuit 
to  its  normal  condition.  The  purpose  of  the  ground  connection  on 
each  side  of  the  trunk  circuit  is  to  disconnect  the  automatic  switches. 
Relay  D  in  the  trunk  circuit  is  provided  with  a  copper  shell  over  the 
iron  core,  which  makes  it  sluggish  in  action.  This  is  necessary  so 
that  it  will  not  release  before  armature  2  of  relay  C  has  fallen  back, 
which  will  prevent  the  reestablishment  of  the  circuit  through  this 
relay. 

When  the  toll  call  originates  with  an  automatic  subscriber,  the 
procedure  is  naturally  different.  The  toll  board  is  provided  with  a 
number  of  recording  trunks  which  are  connected  to  the  automatic 
switches  in  a  manner  similar  to  that  of  a  subscriber's  line.  When  an 
automatic  subscriber  wishes  to  make  a  toll  call,  he  selects  the  number 
marked  "  toll  "  on  his  dial  and  presses  the  ringing  key.  The  operation 
of  the  dial  causes  the  automatic  switches  to  select  an  idle  recording 
trunk.  Fig.  70  shows  a  diagram  of  this  trunk  circuit.  The  operation 
of  the  ringing  key  will  allow  current  to  flow  through  the  recording 
trunk  relay,  thereby  completing  a  circuit  through  the  locking  winding, 
which  will  hold  the  relay  in  an  operated  position  until  the  ground 
connection  is  removed  by  the  insertion  of  the  answering  plug.  The 
operation  of  the  relay  also  completes  a  circuit  through  the  lamp 
signal,  which  will  attract  the  recording  operator's  attention.  When 
the  operator  plugs  into  the  recording  jack  the  lamp  will  be  extinguished. 


162 


TOLL  TELEPHONE  PRACTICE 


She  will  then  actuate  her  listening  key  and  upon  ascertaining  the  details 
of  the  call  will  tell  the  subscriber  to  hang  up  his  receiver  and  wait  until 


FIG.  70.  —  Diagram  of  a  Recording  Toll  Trunk,  at  Dayton,  Ohio. 

called.  The  toll  ticket  is  then  passed  to  a  line  operator,  who  completes 
the  call  in  the  manner  described  in  connection  with  the  circuit  shown 
in  Fig.  69. 

Toll  boards  used  in  connection  with  automatic  local  exchanges  are 
usually  equipped  with  one  or  two  positions  for  handling  the  rural 
business.  In  the  Dayton  boards  these  connections  are  dealt  with  in 

RURAL  LINE  POSITION  TOLL.  LINE:  POSITIONS 


FIG.  71. 


Diagram  of  a  Toll  Board  Trunk  from  a  Line  Position  to  a  Rural  Position,  at 
Dayton,  Ohio. 


the  same  manner  as  the  toll  connections.  When  a  toll  subscriber 
desires  a  rural  connection,  however,  the  call  must  be  trunked  to  the 
rural  position  because  the  rural  lines  are  not  multipled.  Fig.  71  shows 
the  trunk  used  for  this  class  of  service.  When  the  toll  operator 
receives  a  call  for  a  rural  subscriber  she  will  communicate  over  her 
order  circuit  with  the  rural  operator,  giving  the  latter  the  number 


TOLL  CONNECTIONS  TO  LOCAL  AUTOMATIC  SYSTEMS  163 


1 64  TOLL  TELEPHONE  PRACTICE 

of  the  subscriber  desired.  The  rural  operator  in  turn  assigns  the  trunk 
and  inserts  the  plug  in  the  jack  of  the  called-for  line.  This  will  light 
the  disconnect  lamp  associated  with  the  trunk  at  the  rural  position. 
The  lamp  will  be  extinguished,  however,  as  soon  as  the  toll  operator 
takes  up  the  trunk.  She  then  rings  the  rural  subscriber  in  the  usual 
way.  When  the  conversation  has  been  completed  and  the  toll  operator 
has  received  the  disconnect  signal,  she  will  take  down  the  connection 
and  thereby  complete  a  circuit  through  the  disconnect  lamp  at  the 
rural  operator's  position.  This  operator,  upon  seeing  the  disconnect 
signal,  will  remove  the  trunk  plug,  thereby  releasing  the  relay  and 
opening  the  lamp  circuit. 

The  toll  circuits  designed  by  the  Automatic  Electric  Company  for 
small  toll  installations  merit  a  special  description,  inasmuch  as  they 
do  not  correspond  exactly  with  any  of  the  systems  described  before. 
Fig.  72  shows  their  toll-to-automatic  connection.     It  will  be  observed 
that  the  cord  circuit  is  of  the  lamp  signal  type,  while  the  line  is  of 
the  drop  type.     These  circuits  are  very  similar  to  those  described  in 
the  two  preceding  chapters.     The  ground  connection  for  operating  the 
cut-off  relay,  the  supervisory  lamp  and  the  locking  winding  of  the  cord 
relay  is  obtained  in  this  case  through  a  make  contact  on  the  multiple 
line  jack.     While  this  is  a  very  ingenious  scheme,  it  is  questionable 
whether  the  saving  in  relays  is  not  offset  by  the  cost  of  the  additional 
contacts  in  the  jacks,  and  the  extra  wiring.     The  operation  of  the 
circuit,  with  the  exception  of  a  few  variations  in  the  trunks,  is  practi- 
cally the  same  as  that  at  Dayton.     It  will  be  noted  that  when  the  plug 
is  inserted  in  the  trunk  jack,  a  circuit  is  established  from" the  ground 
on  the  make  contact  at  the  jack,  through  relays  A  and  B  to  battery, 
thus  energizing  the  relays.  "When  the  operator  withdraws  the  plug, 
these  relays  are  released  and  this  serves  to  release  the  automatic 
switches.     The  armatures  of  relay  A  fall  back  immediately,  but  as 
relay  B  is  slow-acting  it  continues  to  hold  its  armatures  for  a  short 
interval,  thereby  connecting  ground  to  each  side  of  the  trunk,  which 
serves  to  release  the  automatic  switches.     The  operation  of  this  cir- 
cuit depends  upon  the  slow  action  of  relay  B.     It  would  seem  that 
this  feature  of  the  circuit  is  somewhat  marginal,  while  the  circuit  shown 
in  Fig.  69  is  positive  in  its  action  because  the  ground  connection  is 
necessary  to  release  the  trunk  relays.     Key  7  is  used  to  prevent  a 
disconnect  at  the  switches  in  case  the  operator  should  wish  to  change 
cords. 


CHAPTER  X 

SUPERVISORY   EQUIPMENT   AND   TOLL   CHIEF 
OPERATOR'S   DESK 

THE  requirements  of  toll  operating  are  ordinarily  much  more  exacting 
than  those  of  local  operating  and  the  personnel  of  the  operating  force 
should  be  correspondingly  better.  The  need  for.  supervision,  at  a  toll 
board,  is  especially  prominent  because  of  the  comparatively  complex 
nature  of  the  operator's  work;  and  of  course  the  reasons  which  make 
supervision  so  essential  in  local  operating  are  present  also  in  this  case. 
The  operating  room  organization  nominally  consists  of  a  chief  oper- 
ator in  charge,  a  group  of  immediate  subordinates  who  are  termed 
monitors,  or  supervisors,  and  under  each  of  the  latter  a  group  of 
operators. 

The  chief  operator  is  essentially  an  executive  in  all  but  the  small 
offices,  where  she  probably  assumes  also  the  duties  of  a  supervisor. 
The  work  of  real  supervision  falls  naturally  on  the  supervisors.  Each 
supervisor  has  charge  of  a  subdivision  of  the  operating  force  and  is 
responsible  in  her  division  for  the  prompt  dispatch  of  traffic,  under 
the  rules,  and  the  enforcement  of  discipline.  The  routine  work  of  the 
supervisor  consists  largely  of  overseeing  her  operators,  watching  for 
and  preventing  unnecessary  delays,  giving  personal  help  as  needed  and 
occasionally  handling  calls  herself  when  irregularities  arise. 

Supervision  in  general  is  of  two  kinds,  one  of  which  has  just  been 
described;  the  other  is  of  a  secret  character,  effected  by  means  of 
listening  circuits  connected  to  toll  lines,  trunks  and  operators'  tele- 
phone circuits.  The  latter  naturally  requires  special  equipment, 
varying  according  to  the  size  and  needs  of  each  office.  This  chapter 
deals  particularly  with  such  equipment  and  its  arrangement.  There 
is  also  some  equipment  for  the  use  of  the  chief  operator  and  the  super- 
visors in  routine  work,which  will  be  included  in  the  following  treatment. 

The  supervisor's  equipment  is  very  simple,  consisting  of  a  breast- 
plate transmitter  and  head  receiver,  which  she  wears  continually 
while  on  duty.  She  is  always  ready,  therefore,  to  plug  into  an  oper- 

165 


1 66  TOLL  TELEPHONE  PRACTICE 

ator's  jack  and  take  up  a  situation  which  the  operator  herself  is 
incapable  of  handling.  However,  since  the  supervisor  is  normally 
passing  back  and  forth  behind  her  group  of  operators,  it  becomes 
necessary  to  have  some  scheme  whereby  an  operator  can  attract  the 
supervisor's  attention  if  necessary.  For  this  purpose,  the  board  is 
equipped  with  a  supervisor's  trunk,  which  is  a  special  line  multipled 
through  that  portion  of  the  board  comprising  the  supervisor's  division. 
This  circuit  is  equipped  with  any  suitable  calling  device  of  the  audible 
type,  which  is  mounted  at  some  convenient  place  on  the  wall  of  the 
operating  room.  When  any  operator  desires  the  aid  of  the  super- 
visor, she  will  plug  into  the  supervisor's  trunk  jack  and  ring.  This 
will  attract  the  attention  of  the  supervisor,  who  will  answer  by  inserting 
her  telephone  plug  in  the  jack  of  a  special  equipment  conveniently 
located  in  her  part  of  the  operating  room.  This  equipment  may  be 
either  separate  entirely  /from  the  board,  as  shown  by  the  pedestals 
in  the  frontispiece,  or  it  may  be  connected  to  jacks  located  in  the  key- 
shelf  rail.  When  several  supervisor's  circuits  are  installed,  the  audible 
signals  are  made  distinctive,  so  as  not  to  be  confusing.  Where  the 
toll  board  is  a  small  equipment,  say  of  four  or  five  positions,  the  super- 
visor can  readily  be  called  without  the  use  of  special  apparatus;  but 
in  a  large  office  some  systematic  method  of  calling,  such  as  the  one 
described,  is  necessary  to  avoid  confusion  and  disturbance. 

The  circuit  shown  in  Fig.  73  illustrates  a  supervisor's  trunk  that 
has  been  used  quite  extensively  and  will  serve  as  an  example  of  the 
type  of  equipment  required  for  such  work.  A  detailed  description 
of  the  operation  of  this  circuit  follows.  When  an  operator  desires  to 
call  her  supervisor,  she  inserts  the  answering  plug  of  a  pair  of  cords 
in  the  supervisor's  trunk  multiple  jack,  and  then  rings.  This  will 
naturally  actuate  the  bell  B,  which  is  bridged  directly  across  the  tip 
and  ring  strands  of  the  trunk  circuit,  and  the  supervisor  will  thereupon 
insert  her  telephone  plug  in  the  nearest  answering  jack.  However, 
should  the  supervisor  be  engaged  and  thus  not  able  to  give  the  call 
immediate  attention,  the  toll  operator  may  proceed  with  other  work, 
since  the  supervisory  lamp  associated  with  the  cord  used  in  calling 
will  light  as  soon  as  the  plug  is  inserted  in  the  trunk  jack,  and  it  will 
remain  lighted  until  the  supervisor  answers,  or  the  plug  is  withdrawn 
from  the  jack.  The  insertion  of  this  plug  completes  a  circuit  which 
may  be  traced  as  follows:  from  ground  through  one  winding  of  relay 
4,  to  the  break  contact  and  the  armature  A  of  relay  3,  over  the  tip 


SUPERVISORY  EQUIPMENT 


I67 


l68  TOLL  TELEPHONE  PRACTICE 

side  of  the  trunk  and  the  answering  cord,  thence  through  relay  i  to 
the  ring  strand  of  the  cord  and  the  trunk,  by  way  of  the  armature  and 
the  break  contact  of  relay  3,  through  the  other  winding  of  relay  4  and 
then  to  battery.  The  completion  of  this  circuit  will  energize  relays 
i  and  4.  The  actuation  of  relay  i  closes  a  circuit  which  can  be  traced 
from  battery  through  the  supervisory  lamp,  the  armature  and  the 
make  contact  of  the  relay  and  through  the  break  contact  of  key  4  to 
ground.  This  will  light  the  supervisory  lamp.  As  soon  as  the  super- 
visor inserts  the  plug  of  her  set,  a  circuit  will  be  completed  which  can 
be  traced  from  the  ground  on  the  make  spring  of  the  telephone  jack 
through  relay  3  to  battery.  The  operation  of  relay  3  will  open  the 
supervisory  relay  circuit  outlined  above,  which  in  turn  will  release 
relay  i.  The  supervisory  lamp  in  the  cord  circuit,  therefore,  will  be 
extinguished  thereby  informing  the  toll  operator  that  the  supervisor 
has  answered.  The  operator  then  actuates  her  listening  key,  thus 
completing  the  talking  circuit.  When  the  conversation  is  completed, 
listening  key  2  will  be  restored  to  normal  and  the  plug  of  the  super- 
visor's set  removed  from  the  jack;  this  will  relight  the  supervisory 
lamp  in  the  cord  circuit.  The  lamp  will  remain  lighted  until  the 
operator  takes  down  the  connection,  which  will  restore  the  apparatus 
to  its  normal  condition.  The  talking  circuit  is  of  the  standard  type 
used  with  the  breastplate  equipment  and,  therefore,  can  be  passed 
without  further  comment. 

Relay  4  of  the  circuit  performs  a  double  function;  it  not  only  feeds 
current  to  relay  i  hi  the  cord  circuit,  but  the  attraction  of  its  armature 
completes  the  battery  circuit  through  the  busy  lamps,  thus  notifying 
the  other  operators  that  this  trunk  line  is  in  use.  As  soon  as  the 
supervisor  inserts  the  listening  plug  in  the  answering  jack,  relay  3  is 
operated,  which  thereby  releases  relay  4.  This  will  not  extinguish 
the  busy  lamps  because  the  circuit  is  now  completed  by  armature  C 
of  relay  3.  Consequently  the  busy  lamps  never  allow  the  circuit  to 
remain  unguarded,  for  as  soon  as  the  toll  operator  inserts  a  plug  in 
any  one  of  the  trunk  multiple  jacks  the  busy  lamps  will  light,  and  they 
will  remain  lighted  as  long  as  a  plug  remains  in  either  jack. 

The  equipment  for  a  chief  operator's  position  is  much  more  com- 
plicated than  that  just  described  for  a  supervisor,  and  is  generally 
installed  in  a  desk  which  is  so  situated  as  to  give  the  chief  operator  a 
clear  view  of  the  entire  operating  room.  However,  in  a  very  large 
toll  office,  the  chief  operator's  duties  are  of  such  a  character  that  she 


SUPERVISORY  EQUIPMENT 


169 


is  given  a  private  office;  in  that  case  she  usually  leaves  the  details  of 
supervision  and  discipline  in  charge  of  an  assistant.  In  such  cases 
the  chief  operator  devotes  her  entire  tune  to  the  general  management 
of  the  operating  force,  such  as  employing  new  operators,  preparing 
reports,  attending  to  complaints  and  keeping  records  of  the  individual 
work  and  conduct  of  the  operating  force. 

In  the  smaller  exchanges  it  is  considered  good  practice  to  keep  the 
chief  operator  in  the  operating  room,  so  that  she  will  be  always  in 
touch  with  the  details  of  operation.  The  chief  operator's  desk  is 
equipped  with  circuits  and  apparatus  by  means  of  which  she  can 
instantly  reach  any  operator  in  the  room,  either  to  speak  to  her  or  to 
observe  the  manner  in  which  she  is  handling  her  work.  In  the  follow- 
ing description  these  circuits  will  be  considered  individually  and  a 
detailed  analysis  will  be  given  of  the  operation  of  each. 

Fig.  74  shows  a  circuit  giving  the  necessary  connections  for  chief 
operator's  listening  and  monitoring  taps.  It  will  be  noted  that  the 


CHIEF  OPRS.  DESK 

ICUT-OUT 


TOLL  OP'RS.  POSITION 


FIG.  74.  —  Diagram  of  Chief  Operator's  Listening  and  Monitoring  Taps. 

chief  operator's  end  of  the  circuit  terminates  in  a  double -throw  key 
of  the  cam  type,  which  results  in  a  very  neat  and  compact  arrangement. 
There  are  many  desks  in  which  these  taps  terminate  in  spring  jacks, 
thus  necessitating  the  use  of  a  cord  and  plug  to  complete  a  connection. 
This  is  not  as  convenient  as  the  arrangement  shown  in  the  figure. 
In  the  wiring  of  the  chief  operator's  tap,  the  induction  coil  at  each 
operator's  position  must  be  equipped  with  a  tertiary  or  third  winding 
for  secret  supervision.  This  circuit  is  used  when  the  chief  operator 
wishes  to  listen  to  any  conversation  that  the  toll  operator  may  be 
engaged  in,  without  the  operator's  knowledge.  The  theory  upon  which 
the  operation  of  this  circuit  is  founded  may  be  compared  to  the  opera- 
tion of  a  transformer  with  an  open-circuited  secondary. 


170  TOLL  TELEPHONE  PRACTICE 

It  is  a  well-established  principle  of  transformer  action  that  when  the 
secondary  circuit  is  open,  that  is,  of  infinite  resistance,  the  current 
flowing  in  the  primary  meets  the  full  primary  impedance.  This  is 
due  to  the  fact  that  the  flux  set  up  in  the  core  of  the  transformer  by 
the  current  flowing  through  the  primary  produces  a  counter  electro- 
motive force  in  the  primary  winding  which  limits  the  flow  of  current. 
But  when  the  secondary  circuit  of  the  transformer  is  closed  the  current 
in  the  primary  will  increase,  due  to  the  current  flowing  in  the  secondary 
which  cuts  down  the  counter  electromotive  force  referred  to  above. 

In  the  case  at  hand,  the  induction  coil,  or  transformer  as  it  may  be 
called,  has  three  windings,  the  primary  winding  of  low  resistance  and 
few  turns,  the  secondary  winding  of  higher  resistance  and  a  greater 
number  of  turns,  and  the  tertiary  winding  of  still  higher  resistance 
and  a  still  greater  number  of  turns.  It  is  obvious,  first,  that  when  the 
toll  operator  is  talking,  the  primary  coil  is  the  one  producing  the 
fluctuations  of  magnetic  flux  in  the  core,  which  act  on  the  secondary 
and  tertiary  windings  of  the  coil;  and  secondly,  when  the  subscriber 
is  talking,  the  secondary  coil  produces  the  fluctuations,  which  in  turn 
act  on  the  primary  and  tertiary  windings.  But  the  tertiary  circuit 
contains  no  source  of  E.M.F.  and  it  therefore  produces  no  impulses 
in  the  primary  or  secondary  when  it  is  opened  and  closed.  A  very 
slight  click  can  be  observed  under  favorable  conditions,  but  it  is 
probably  due  to  the  effects  of  electrostatic  capacity  between  the 
windings.  Ordinarily  the  click  cannot  be  observed.  In  order  to  make 
certain  that  the  operator  cannot  detect  supervision,  a  primary  cut- 
out key  is  installed  in  the  chief  operator's  telephone  set,  to  prevent 
the  picking  up  of  room-noise  or  disturbance. 

The  monitor's  tap,  as  shown  in  Fig.  74,  is  wired  in  parallel  with  the 
toll  operator's  talking  set;  and,  therefore,  when  the  monitoring  key 
is  actuated,  the  chief  operator  can  speak  to  the  operator  and  give  her 
such  instruction  or  aid  as  may  be  required.  By  means  of  this  circuit, 
the  chief  operator  can  connect  instantly  with  any  operator  and  thus 
avoid  the  delay  which  would  naturally  arise  if  she  were  required  to 
use  a  trunk  circuit. 

Another  scheme  which  helps  to  reduce  the  work  of  the  chief  oper- 
ator is  the  so-called  instruction  circuit.  This  circuit  is  shown  in  Fig. 
75  and  is  used  by  the  chief  operator  when  she  desires  to  issue  general 
instructions  to  several  or  all  of  the  operators,  simultaneously.  The 
operation  of  this  circuit  is  briefly  as  follows.  When  the  chief  operator 


SUPERVISORY  EQUIPMENT 


171 


desires  to  issue  general  instructions,  she  will  operate  the  instruction 
key,  which  not  only  bridges  her  telephone  set  across  the  trunk  line, 
but  also  completes  a  circuit  through  relay  A ;  the  operation  of  the  relay 
establishes  a  circuit  through  the  instruction  lamp  at  each  toll  operator's 
position.  When  this  signal  appears,  the  operator  knows  that  general 
instructions  are  to  be  issued  and  she  consequently  operates  her  in- 
struction key.  This  extinguishes  the  instruction  lamp  and  at  the 


CHIEF  OPRS.  DESK 


OTHER  TOLL  OPRS. 
POSITIONS 


FIG.  75.  —  Chief  Operator's  Instruction  Circuit. 

same  time  bridges  her  telephone  set  across  the  trunk  circuit.  The 
chief  operator  may  have  one  of  these  circuits  for  each  group  of  three 
or  four  sections,  thereby  enabling  her  to  instruct  six  or  eight  operators 
at  a  time;  or  the  circuit  may  be  common  to  the  entire  board.  The 
utility  of  this  circuit  is  self-evident,  for  it  is  a  means  of  giving  new 
instruction  to  all  operators  instantly. 

Another  circuit  which  good  practice  places  at  the  chief  operator's 
desk  is  the  interposition  trunk.  This  circuit  has  previously  been 
described  in  Chapter  VIII.  It  is  almost  unnecessary  to  point  out  that 
these  circuits  afford  a  temptation  to  the  operators  to  carry  on  personal 
conversations.  To  avoid  the  abuse  of  these  circuits,  they  should  be 
multipled  at  the  chief  operator's  desk  and  preferably  be  equipped  with 
visual  busy  signals,  for  convenience  in  supervision. 

The  circuits  which  show  the  promptness  with  which  the  operators 
at  the  board  are  handling  connections,  are  the  line  and  supervisory 
pilot  taps.  These  circuits  are  shown  in  Fig.  76,  from  which  it  will  be 
observed  that  the  pilot  lamps  in  each  position  are  multipled  in  the 
chief  operator's  desk.  Therefore,  whenever  a  call  is  received  at  any 
particular  position,  both  the  line  pilot  lamp  at  the  position  and  the 
corresponding  lamp  at  the  chief  operator's  desk  will  light;  in  case  the 


172 


TOLL  TELEPHONE  PRACTICE 


lamp  remains  lighted  longer  than  a  proper  interval,  the  chief  operator 
will  cut  in  on  the  monitor's  tap  and  determine  the  cause.  The  same 
applies  if  the  supervisory  pilot  lamp  remains  lighted  too  long. 


CHIEF  OPRS.  DESK 


TOLL  OP'R'S.  POSITION 


FIG.  76.  —  Chief  Operator's  Pilot  Taps. 

In  all  exchange  work  more  or  less  trouble  is  experienced  from 
improper  listening  by  the  operators.  In  some  instances  the  rules  have 
been  so  strict  as  to  cause  the  discharge  of  an  operator  detected  in  so 
doing.  To  assist  the  chief  operator  in  watching  operators  who  are 
suspected  of  this  practice,  her  desk  is  sometimes  equipped  with  a 
circuit  similar  to  the  one  shown  in  Fig.  77.  The  lamp  at  the  desk  end 

|  TOLL  QpWs.  POSITION 


IEF  OFRS.PESK 

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FIG.  77.  —  Chief  Operator's  Tell-tale  Circuit. 

of  the  circuit  will  light  whenever  a  bridged  listening  key  is  thrown  in 
any  cord  circuit  of  a  given  position.  If  this  lamp  lights  and  remains 
lighted  for  some  time,  the  chief  operator's  suspicions  will  be  aroused 
and  she  will  operate  her  tap  key,  which  permits  her  to  listen  to  the 
conversation  without  attracting  the  attention  of  the  operator. 

While  the  wiring  of  these  circuits  is  quite  simple,  it  is  often  a  difficult 


SUPERVISORY  EQUIPMENT  173 

problem  to  determine  the  best  method  of  carrying  the  leads  from  the 
various  toll  operators'  positions  to  the  chief  operator's  desk.  A  con- 
venient method  of  handling  the  pilot  and  listening  taps  is  to  carry 
the  wires  from  the  various  positions  to  some  common  point,  such  as 
the  first  position  of  the  board,  where  they  should  be  connected  to  a 
suitable  connecting  rack.  They  may  then  be  carried  in  a  factory- 
made  cable,  through  a  duct  under  the  floor,  to  the  desk.  It  is  always 
advisable  to  have  the  various  ducts  between  the  desk,  the  main  board 
and  the  frames  installed  during  the  construction  of  the  building;  but 
as  exchanges  are  not  always  installed  in  new  buildings,  this  is  fre- 
quently impossible.  Consequently  the  installer,  at  times,  meets  with 
some  very  trying  conditions,  especially  where  the  floors  in  the  building 
are  of  tile  or  cement. 

Some  engineers  specify  that  all  taps  shall  be  carried  to  the  inter- 
mediate distributing  frame.  However,  this  seems  unnecessary  for 
the  pilot  and  listening  taps,  since  there  is  very  little,  if  anything,  to 
be  gained  by  such  procedure;  in  nearly  all  cases  the  cables  which  carry 
these  taps  must  be  taken  back  over  the  same  route  before  they  enter 
the  duct  leading  to  the  desk.  The  only  real  advantage  in  having 
these  taps  looped  through  the  intermediate  distributing  frame  is 
convenience  in  testing;  but  with  circuits  as  simple  as  these,  the  testing 
which  will  be  required  after  the  board  is  put  into  operation  is  almost 
negligible. 

It  will  be  noted  that  all  the  circuits  described  above  were  de- 
signed for  key-equipped  desks,  in  place  of  jacks  and  cords.  The 
reason  for  this  is  obvious;  it  is  a  well-known  fact  in  switchboard 
operation  that  the  cord  is  the  weakest  part  of  the  equipment,  and 
moreover,  the  key-equipped  desk  offers  an. additional  advantage  in 
the  respect  that  it  requires  no  equipment  on  the  top  of  the  desk,  thus 
giving  the  chief  operator  ample  writing  space.  When  all  the  circuits 
ordinarily  equipped  with  jacks  are  provided  instead  with  keys,  the 
equipment  is  placed  in  a  turret  which  is  mounted  on  the  top  of  a  flat- 
top desk,  thus  making  a  very  neat  and  compact  arrangement. 

In  addition  to  what  has  been  said  regarding  the  chief  operator's 
desk,  it  might  be  well  to  add  in  conclusion  that  space  is  usually  pro- 
vided for  pigeon  holes  and  bookstalls.  It  is  also  customary  to  furnish 
the -desk  with  card  filing  cases.  These  are  located  in  the  drawers  or 
in  neat  receptacles  arranged  in  the  top  of  the  desk  in  such  a  manner 
that  the  cards  are  flush  with  the  top  of  the  writing  shelf. 


CHAPTER  XI 
TOLL  WIRE  CHIEF'S  DESK 

SATISFACTORY  means  must  be  provided  for  making  the  necessary  line 
and  switchboard  tests  in  toll  as  well  as  in  local  systems.  There  are 
two  general  methods  of  accomplishing  this  purpose ;  first,  by  means  of 
a  suitable  testing  equipment  at  the  test  panel;  and  secondly,  by  the 
use  of  an  entirely  separate  equipment  known  as  the  "  wire  chief's 
desk." 

The  first  of  the  methods  above  mentioned  is  nearly  universal 
practice  in  offices  of  considerable  size  and  this  is  especially  true  of  the 
American  Telephone  and  Telegraph  Company's  plant,  since  most  of 
their  lines  are  either  composited,  simplexed  or  phantomed.  Special 
apparatus  must  be  connected  to  the  circuit  when  a  telephone  line  is 
to  be  used  for  any  of  these  additional  purposes  and  this  is  best  ac- 
complished by  wiring  the  line  through  special  spring  jacks  provided 
for  the  purpose  at  the  test  panel.  As  this  spring-jack  equipment  is 
essentially  the  same  for  line  testing  as  for  the  latter  purpose,  it  is 
undoubtedly  better  and  more  economical  practice  to  do  all  testing  at 
the  panel.  Some  engineers  maintain  that  the  installation  of  a  wire 
chief's  desk,  in  addition  to  a  test  panel,  is  essential;  but  since  the  pioneer 
in  this  field,  the  American  Telephone  and  Telegraph  Company,  has 
not  adopted  it  to  any  extent,  it  will  be  best  to  examine  the  question 
carefully  in  the  light  of  individual  requirements.  Telephone  com- 
panies whose  lines  connect  only  the  smaller  towns  and  on  whom  the 
demand  for  morse  service  is  very  limited,  do  not  require  a  morse 
panel.  The  wire  chief's  desk  finds  a  proper  and  logical  place  in  these 
offices,  for  there  the  desk  serves  the  double  purpose  of  a  testing  equip- 
ment and  a  morse  panel,  as  the  amount  of  telegraph  work  is  so  limited 
that  it  can  be  handled  readily  by  the  wire  chief  personally. 

The  wire  chief's  desk  should  be  located  in  a  position  that  will  make 
the  distributing  frames  and  the  other  apparatus  in  the  terminal  room 
as  accessible  as  possible,  thereby  reducing  his  work  to  a  minimum. 
It  is  also  very  essential  that  the  toll  equipment  be  wired  so  that  the 

174 


TOLL  WIRE  CHIEF'S  DESK  175 

wire  chief  can  readily  and  speedily  connect  his  testing  apparatus  to 
any  toll  line  entering  the  office.  In  toll  work  this  is  accomplished  in 
two  ways.  The  first  and  most  satisfactory  method  is  to  multiple  the 
toll  lines  through  the  desk  by  means  of  cut-off  jacks,  which  concen- 
trates all  the  lines  at  this  point;  the  second  method  employs  direct 
trunks  to  the  toll  board  and  the  test  panel.  The  first  method  adds 
additional  line  resistance  by  virtue  of  the  cable  necessary  to  wire  the 
lines  to  and  from  the  desk,  and  further,  the  additional  jack  contacts 
increase  the  probability  of  trouble.  The  second  method  is  slow  be- 
cause the  wire  chief  must  procure  the  aid  of  an  operator  in  setting 
up  a  test  connection.  However,  in  all  but  the  larger  exchanges,  one 
person  can  readily  handle  all  panel  connections  in  addition  to  making 
the  usual  tests;  and,  therefore,  it  is  much  more  convenient  in  such 
cases  to  have  the  combined  equipment. 

The  testing  equipment  furnished  for  a  wire  chief's  desk  is  practically 
identical  with  that  furnished  at  the  test  panel;  but  the  arrangement 
is  not  the  same  and  the  circuits  are  different  due  primarily  to  the  fact 
that  more  attention  is  given  to  making  satisfactory  tests  of  the  office 
equipment. 

The  more  important  circuits  furnished  at  the  desk  are  the  testing 
cord,  which  is  equipped  with  the  necessary  keys,  voltmeters  and 
morse  instruments  for  making  all  tests  incidental  to  the  proper 
maintenance  of  the  toll  lines;  the  trunks  to  the  toll  boards,  terminating 
at  that  point  in  cords  and  plugs,  so  as  to  furnish  ready  means  for 
testing  through  the  toll  board;  and  similar  trunks  wired  to  the  arrester 
side  of  the  main  distributing  frame,  for  testing  in  or  out.  Lines  to  the 
other  desks  in  the  office  should  also  be  furnished. 

The  design  of  the  various  desk  circuits  is  dependent,  to  some  extent, 
on  the  type  of  circuits  used  at  the  toll  board;  but  the  ultimate  results 
to  be  accomplished  are  identical  in  any  case.  Flexibility  in  these  cir- 
cuits is  of  paramount  importance;  a  desk  may  be  equipped  with  the 
best  of  testing  instruments  and  other  apparatus,  and  yet  the  wire 
chief  may  find  it  practically  impossible,  or  at  least  extremely  awkward, 
to  make  certain  tests,  because  of  the  faulty  circuit  design.  The 
circuits  which  are  shown  in  the  following  diagrams  are  designed  to 
operate  in  conjunction  with  a  lamp  signal  switchboard.  These  circuits 
can  be  adapted,  with  but  slight  changes,  to  any  type  of  board,  the 
lamp  signal  equipment  being  chosen  for  illustration  because  it  repre- 
sents the  best  and  most  modern  toll  practice. 


1  76  TOLL  TELEPHONE  PRACTICE 

The  desk  wiring  of  a  toll  line  is  shown  in  Fig.  78.  It  will  be  observed 
that  the  line  is  wired  direct  from  the  main  distributing  frame  to  a  pair 
of  cut-off  jacks  i  and  2  at  the  desk  and  is  then  looped  to  jacks  3  and 
4;  from  there  it  is  cabled  to  the  intermediate  distributing  frame,  and 
then  cross-connected  to  the  switchboard  terminals.  The  reason  for 
connecting  the  jacks  as  shown  will  be  given  with  the  narrative  of 
operation  of  the  testing  circuit.  Many  schemes  of  wiring  the  line 
circuit  have  been  devised.  Another  method  is  to  carry  the  lines  from 


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FIG.  78.  —  Wiring  of  Toll-line  Circuit  at  Wire  Chief's  Desk. 

the  main  distributing  frame  direct  to  the  intermediate  frame,  from 
which  point  they  are  looped  through  the  desk.  The  object  of  the 
latter  arrangement  is  to  provide  means  for  cutting  the  wire  chief's 
loop  out  of  circuit.  This  is  readily  accomplished  by  switching  the 
jumper  wires  at  the  intermediate  frame  direct  to  the  switchboard 
terminals,  in  place  of  the  desk  terminals.  The  advantage  of  this 
scheme  comes  into  play  when  trouble  develops  in  the  cable  or  jacks 
in  the  desk  loop;  but  since  the  probability  of  this  is  extremely  rare 
in  so  simple  a  circuit,  it  is  doubtful  whether  this  wiring  is  a  profit- 
able investment.  Furthermore,  the  additional  cable  required  for  this 
wiring  increases  the  line  resistance  to  some  extent,  and  this  is  objec- 
tionable in  case  no  direct  benefit  results.  One  of  the  fundamental 
principles  of  toll  board  design  consists  in  keeping  the  office  resistance 
of  the  line  as  low  as  possible. 

The  jacks  shown  in  Fig.  78  can  be  arranged  in  the  desk  in  two 
general  ways.  The  first  of  these  methods  is  to  place  the  four  jacks 
associated  with  any  one  line  in  a  vertical  row.  These  jacks  are  usu- 
ally mounted  twenty  per  strip,  four  strips  being  used  for  each  twenty 
lines.  This  arrangement  of  jacks  and  the  general  face  equipment  of 
a  one-position  desk  are  shown  in  Fig,  79.  The  second  method  of  jack 


TOLL  WIRE   CHIEF'S  DESK 


177 


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TOLL  TELEPHONE  PRACTICE 


arrangement  is  shown  in  Fig.  80,  in  which  the  jacks  are  mounted  in 
pairs.  Both  methods  are  in  general  use  and  there  is  very  little  choice 
between  them. 

Reference  will  now  be  made  to  the  testing  circuit  shown  in  Fig.  81. 
At  first  glance  this  circuit  will  appear  rather  complicated;  but  upon 

Our   IN 


FIG.  80.  —  Arrangement  of  Jacks  at  Wire  Chief's  Desk. 

closer  investigation,  it  will  be  observed  that  it  is  composed  of  several 
simple  circuits,  combined  for  convenience  in  operating  and  for  the 
greatest  possible  reduction  of  the  amount  of  equipment  required. 
The  operation  of  this  circuit  is  briefly  as  follows.  When  the  wire 
chief  desires  to  make  a  test  on  a  toll  line,  he  will  insert  the  tip  and 
ring  plugs  of  the  test  circuit  in  the  corresponding  pair  of  "in"  and 


FIG.  8 1.  —  Wire  Chief's  Testing  Circuit. 

"  out "  jacks  which  are  shown  in  Fig.  78;  the  latter  circuit  will  have 
to  be  referred  to  in  conjunction  with  the  test  circuit  to  get  a  clear 
understanding  of  the  operation.  It  is  immaterial  which  pair  of 
jacks  is  used  with  this  test,  as  means  are  provided  in  the  testing 
circuit  itself  to  switch  the  testing  apparatus  to  the  line  or  to  the 
switchboard.  In  what  follows  it  will  be  assumed,  for  the  sake  of 
clearness,  that  the  plugs  have  been  placed  in  the  pair  of  "  out  "  jacks. 
The  insertion  of  the  plugs  in  the  jacks  will  not  open  the  line,  since 


TOLL  WIRE  CHIEF'S  DESK  179 

the  tip  and  ring  conductors  of  each  plug  are  normally  connected  by 
means  of  the  key  wiring  in  the  test  circuit.  These  connections,  for 
each  plug,  can  be  traced  from  the  tip  of  the  plug  through  the  lever  and 
break  springs  of  key  2,  then  successively  through  the  same  springs 
of  keys  3  and  i,  and  thence  to  the  ring  conductor  of  the  same  plug. 
Thus  far  the  test  circuit  merely  fulfills  the  functions  of  the  local  con- 
tacts in  the  line  jacks  themselves,  but  the  wire  chief  may  now  connect 
his  telephone  set  across  the  line,  by  the  operation  of  key  5,  and  thus 
determine  whether  or  not  the  line  is  busy.  This  is  accomplished,  as 
will  be  evident  from  what  has  preceded,  without  in  any  way  disturbing 
the  service;  and  it  also  provides  a  ready  means  of  determining  the 
actual  working  conditions  of  the  line.  If  the  wire  chief,  upon  bridg- 
ing his  telephone  set  across  the  line,  finds  it  not  in  use,  he  can  proceed 
with  the  test  without  fear  of  being  disturbed  from  the  switchboard  end, 
since  the  insertion  of  the  test  plugs  in  the  line  jacks  will  place  battery 
on  the  sleeves;  this  will  cause  the  operation  of  the  cut-off  relay  in  the 
line  circuit,  which  in  turn  will  close  the  circuit  containing  all  the  busy 
signals  at  the  toll  board. 

The  different  keys  in  the  testing  circuit  perform  the  following 
functions : 

Key  i  converts  the  circuit  into  such  form  that  tests  can  be  made 
over  the  tip  plug  in4  conjunction  with  a  testing  trunk  circuit 
which  will  be  fully  explained  in  what  follows. 
Key  2  switches  the  testing  equipment  to  the  "  out  "  line. 
Key  3  switches  the  testing  equipment  to  the  "  in  "  line. 
Key  4  is  the  regular  listening  key. 
Key  5  is  utilized  in  listening-in  on  a  line  quietly,  as  previously 

explained,  that  is,  without  battery. 
Key  6  is  employed  when  it  is  desired  to  place  ringing  current  on 

the  line. 
Key  7  provides  means  for  reversing  the  tip  and  ring  sides  of  the 

circuit,  so  that  either  side  of  the  line  may  be  tested  readily. 
Key  8  is  used  in  connecting  ground  to  one  side  of  the  circuit. 
Key  9  switches  the  voltmeter  into  the  circuit. 
Key  10  connects  the  bridge  to  the  line. 
Key  1 1  switches  the  circuit  from  the  high  to  the  low  scale  of  the 

voltmeter. 

Key  12  connects  the  high-voltage  battery  into  the  voltmeter 
circuit. 


180  TOLL  TELEPHONE  PRACTICE 

Key  13  connects  the  low-voltage  battery  into   the  voltmeter 

circuit. 

Key  14  grounds  one  side  of  the  voltmeter  circuit. 
Keys  15  and  16  are  used  in  performing  certain  bridge  tests. 

The  numbers  used  in  designating  the  various  keys  do  not  indicate 
that  they  are  grouped  in  that  particular  order  in  the  desk,  but  have 
been  used  merely  to  aid  the  explanation.  The  keys  of  a  testing  cir- 
cuit should  be  so  arranged  as  to  best  facilitate  the  work  of  testing. 
For  example,  the  keys  associated  with  the  voltmeter  circuit  should 
be  grouped  together,  and  those  used  in  the  bridge  test  should  form 
another  group. 

The  voltmeter  shown  in  the  circuit  is  almost  always  permanently 
mounted  in  some  convenient  part  of  the  desk,  and  is  usually  placed 
either  in  the  jack  panel  or  in  the  space  immediately  to  one  side  of 
this  panel.  A  portable  type  of  instrument  is  often  used  for  the  pur- 
pose; and  as  these  instruments  are  usually  calibrated  for  horizontal 
operation,  it  is  imperative  to  specify  that  they  shall  be  calibrated  for 
vertical  mounting,  when  placed  as  indicated  in  the  face  equipment 
shown  in  Fig.  79.  The  instrument  best  suited  for  this  work  is  one 
with  a  double  scale,  which  gives  a  wide  range  with  accurate  readings. 
It  is  also  convenient  to  have  a  meter  that  reads  in  each  direction  from 
zero,  which  often  prevents  a  bent  needle;  this  also  makes  the  opera- 
tion faster,  since  no  care  need  be  exercised  in  connecting  the  proper 
polarity  to  the  instrument.  A  meter  having  a  double  scale  of  15-0-15 
and  150-0-150  has  been  found  quite  satisfactory  for  this  class  of 
work;  but  some  prefer  an  instrument  with  a  higher  scale,  such  as 
30-0-30  and  300-0-300. 

The  bridge  used  with  the  test  circuit  should  be  of  the  portable 
type,  as  there  is  no  convenient  place  in  the  desk  for  mounting  it 
permanently.  When  required  in  making  a  test,  it  can  be  placed  on 
the  top  of  the  desk  and  connected  to  the  binding  posts,  which  are 
shown  on  the  face  equipment  in  Fig.  79.  These  posts  may  be  mounted 
either  on  the  key  shelf  or  in  the  face  of  the  board  below  the  volt- 
meter. A  drawer  in  the  lower  part  of  the  desk  is  frequently  designed 
for  storing  the  bridge  when  not  in  use.  Some  wire  chiefs  prefer  to 
have  the  bridge  permanently  wired  and  placed  on  a  separate  table, 
so  that  no  time  will  be  wasted  in  putting  it  into  service. 

Another  convenient  method  of  mounting  the  bridge  is  to  build  a 
shelf  at  the  right-hand  end  of  the  desk,  about  six  inches  below  the 


TOLL  WIRE  CHIEF'S  DESK 


181 


surface  of  the  key  shelf.     This  keeps  the  instrument  within  easy  reach 
of  the  operator  and  at  the  same  time  out  of  the  way. 

Another  testing  circuit  which  is  usually  installed  in  the  wire  chief's 
desk  is  shown  in  Fig.  82.  This  circuit  is  used  for  making  preliminary 
tests,  such  as  determining  whether  a  line  is  grounded,  open  or  crossed. 
The  test  plug  i  shown  in  this  circuit  is  used  only  when  a  test  panel 
is  installed  in  addition  to  a  wire  chief's  desk.  The  function  of  this 
plug  is  to  connect  the  wire  chief's  morse  equipment  to  any  leased 
wire  or  telegraph  line  at  the  test  and  morse  panel.  Thus,  when 


TEST 


FIG.  82.  —  Circuit  for  Preliminary  Tests. 

keys  i,  2  and  3  are  operated,  the  apparatus  connected  to  the  test 
plug  will  be  directly  in  series  with  the  wire  chief's  morse  set.  This 
circuit  can  be  traced  from  the  tip  of  the  test  plug,  through  the  make 
contact  of  key  3,  to  telegraph  relay  R,  thence  through  the  telegraph 
key  and  the  make  contact  of  key  i  to  battery;  while  the  ring  side  of 
the  plug  can  be  traced  to  the  second  make  contact  of  key  3  and  then 
through  the  make  contact  of  key  2  to  ground.  The  tip  and  ring 
plugs  i  and  2,  respectively,  are  used  for  line  tests  at  the  wire  chief's 
desk.  When  these  plugs  are  inserted  in  the  respective  tip  and  ring 
jacks  of  a  toll  line,  the  preliminary  tests  for  a  ground,  an  open  or  a 
cross  can  be  made  as 'follows.  Key  3  remains  in  its  normal  position. 
Then  if  key  i  is  operated,  the  current  will  pass  to  the  tip  line  wire  by 
means  of  the  following  circuit:  from  battery  to  the  make  contacts  of 
key  i ,  through  the  telegraph  key  and  relay  R,  to  the  tip  plug,  out  on 
the  tip  of  the  line,  returning  by  means  of  the  ring  of  the  line,  through 
the  break  contact  of  key  3,  to  the  make  contacts  of  key  2,  and  thence 


182 


TOLL  TELEPHONE  PRACTICE 


to  the  open  break  contacts  of  key  i.  It  must  be  evident,  therefore, 
that  if  a  ground  exists  anywhere  on  the  line,  the  telegraph  relay  R 
will  be  energized,  thus  indicating  the  condition  to  the  wire  chief. 
In  the  test  for  an  open  circuit,  keys  i  and  2  are  both  actuated;  this 
will  complete  a  circuit  from  battery  through  the  telegraph  relay  R, 
to  the  tip  of  the  line  and  thence  back  over  the  ring  of  the  line  to 
ground.  Then,  if  the  line  is  open,  the  telegraph  relay  will  not  oper- 
ate. In  case  a  lineman  has  been  sent  out  to  clear  the  trouble  and  has 
opened  the  circuit  at  the  distant  end,  the  actuation  of  the  telegraph 
relay  will  indicate  that  the  line  wires  are  crossed.  It  might  be  well 
to  explain  that  the  resistance  coil  5,  which  is  in  series  with  the  sounder, 
is  furnished  merely  to  cut  down  the  flow  of  current,  thereby  avoiding 
the  necessity  of  a  low-voltage  battery. 

Thus  far  no  circuits  have  been  shown  by  means  of  which  tests  can 
be  made  directly  from  the  toll  board.     However,  it  is  often  quite 


[     a 

i        /     r 

1  —  k 

u  RELEASE 

k    KEY 
'HOLD 


CALLING*  LAMP 


FIG.  83.  —  Wire  Chief's  Testing  Trunk. 

advisable  to  test  out  a  toll  line  from  the  switchboard;  and  it  is  also 
convenient  at  times  to  trunk  the  wire  chief's  test  circuit,  shown  in 
Fig.  8 1,  to  the  toll  board,  so  that  all  switchboard  apparatus  will  be 
accessible  to  the  testing  circuit.  This  is  accomplished  by  means  of 
the  testing  trunk  shown  in  Fig.  83.  These  trunks  terminate  at  the 
toll  board  in  cords  and  plugs;  and  the  plugs  are  so  placed  that  they 
can  be  inserted  easily  in  the  last  multiple  jack  of  any  line,  thus  en- 
abling the  wire  chief  to  test  the  line  throughout  the  entire  multiple. 
The  operation  of  this  test  trunk  may  be  outlined  as  follows.  When- 
ever any  operator  discovers  a  line  in  trouble,  she  will  immediately 


TOLL  WIRE  CHIEF'S  DESK  183 

report  it  to  the  supervisor  or  the  chief  operator,  who  in  turn  will  fill 
out  a  "  trouble  slip  "  and  send  it  to  the  wire  chief.  At  the  same 
time  she  will  order  the  plug  of  one  of  the  testing  trunks  inserted  in 
the  last  multiple  jack  of  the  line  in  trouble.  The  insertion  of  this 
plug  will  complete  a  circuit  which  is  traceable  from  battery  through 
the  coil  of  relay  A  and  the  springs  of  the  release  key,  to  the  sleeve  of 
the  plug,  thence  to  the  sleeve  of  the  line  jack  and  through  the  cut-off 
relay  to  battery.  The  closing  of  this  circuit  will  cause  the  operation 
of  relay  A  in  the  trunk  and  the  cut-off  relay  in  the  line  circuit.  The 
operation  of  the  latter  will  actuate  all  the  busy  signals  associated 
with  this  line.  The  actuation  of  relay  A  will  complete  two  circuits: 
first,  one  from  ground  to  the  armature  of  the  relay,  then  by  way  of 
the  break  contact  and  the  armature  of  relay  C,  through  the  "  plug- 
ging up  "  lamp  and  thence  to  battery;  second,  a  circuit  from  ground 
by  way  of  armature  i  of  relays  A  and  C,  through  the  springs  of  the 
holding  key  and  the  disconnect  lamp  to  battery.  The  completion  of 
these  two  circuits  will  light  the  disconnect  lamp  at  the  toll  board  and 
the  "  plugging  up  "  lamp  at  the  wire  chief's  desk.  The  wire  chief, 
upon  seeing  the  lighted  lamp,  will  insert  the  tip  testing  plug  of 
the  test  circuit  (shown  in  Fig.  81)  in  the  jack  associated  with  the 
lamp.  This  will  close  a  circuit  which  is  traceable  from  the  battery 
connection  on  the  sleeve  of  the  test  plug,  to  the  sleeve  of  the  trunk  and 
then  by  way  of  the  coil  of  relay  C  to  ground.  Thus  relay  C  will  be 
energized  and  the  attraction  of  armature  i  will  open  the  two  lamp 
circuits  just  traced,  extinguishing  the  signals.  The  wire  chief  will 
now  actuate  key  i  of  the  testing  circuit,  which  will  disconnect  the 
tip  and  the  ring  strands  of  the  cord  from  each  other  and  switch  them 
direct  to  the  tip  and  the  ring  conductors  of  the  test  circuit.  The 
wire  chief  will  then  make  a  preliminary  test  and  in  case  he  finds  the 
switchboard  end  clear,  with  trouble  out  on  the  line,  he  will  operate 
the  holding  key  and  withdraw  the  test  plug  from  the  jack.  The 
operation  of  the  holding  key  will  open  the  disconnect  lamp  circuit, 
previously  described,  and  consequently  prevent  the  re-lighting  of  the 
lamp.  The  "  plugging  up  "  lamp  at  the  desk  will  re-light,  however, 
due  to  the  fact  that  the  withdrawal  of  the  test  plug  will  open  the 
circuit  through  relay  C,  thus  releasing  armature  i  of  the  relay  and 
thereby  closing  the  circuit  through  the  lamp.  The  reason  that  this 
lamp  is  kept  in  a  lighted  condition  is  to  remind  the  wire  chief  that  a 
circuit  is  up  for  test.  The  lineman  can  readily  call  the  wire  chief 


184 


TOLL  TELEPHONE  PRACTICE 


on  this  line  by  ringing  across  the  circuit  with  a  standard  test  set. 
The  alternating  impulses  generated  by  the  test  set  will  seek  a  path 
which  can  be  followed  from  the  ring  of  the  line  to  the  ring  of  the  test 
cord  and  plug,  through  the  break  contact  in  the  jack  at  the  desk, 
through  winding  i  of  relay  B,  thence  by  way  of  armature  2  and  the 
make  contact  of  relay  A,  to  the  tip  break  contact  in  the  desk  jack; 
from  there  it  can  be  traced  to  the  tip  of  the  test  cord  and  back  over 
the  tip  of  the  line.  The  alternating  current  which  flows  in  the  circuit 
just  outlined  will  cause  the  operation  of  relay  5,  which  will  lock. 
This  locking  circuit  can  be  traced  from  the  ground  on  the  armature 
of  the  relay,  through  winding  2,  then  by  way  of  the  break  contact 
and  the  armature  2  of  relay  C,  to  armature  3  and  the  make  contact 
of  relay  A  and  finally  to  battery.  The  attraction  of  the  armature 
of  relay  B  will  also  close  the  circuit  through  the  calling  lamp,  thereby 
attracting  the  attention  of  the  wire  chief.  Relay  5,  when  once  oper- 
ated, will  remain  energized  until  released  by  the  wire  chief.  This 
may  be  done  by  actuating  the  release  key,  which  will  open  the  cir- 
cuit through  the  coil  of  relay  A\  the  release  of  this  relay  will,  in 


ANS 


CAUL. 


FIG.  84.  —  Wire  Chief's  Cord  Circuit. 

turn,  release  relay  B,  at  armature  3  of  the  former.  The  locking  cir- 
cuit will  likewise  be  opened  when  the  wire  chief  plugs  into  the  test 
jack,  since  this  operation  will  energize  relay  C  and  open  the  circuit 
at  armature  2.  The  latter  is  the  usual  method  of  extinguishing  the 
calling  lamp,  since  it  places  the  wire  chief  in  communication  with 
the  lineman.  The  former  method  is  installed  for  auxiliary  purposes 
only.  When  the  trouble  is  cleared,  the  wire  chief  will  remove  the 
test  plug  and  restore  the  holding  key  to  normal,  thereby  lighting  the 


TOLL  WIRE  CHIEF'S  DESK 


185 


disconnect  lamp  at  the  toll  board.  The  operator  in  charge,  upon 
seeing  the  lamp,  will  remove  the  trunk  plug  and  thereby  restore  all 
the  apparatus  to  its  normal  condition. 

Oftentimes  the  wire  chief  will  have  occasion  to  interconnect  two 
lines,  and  for  this  purpose  the  desk  should  be  equipped  with  one  or 


FIG.  85.  —  Two-position  Toll  Wire  Chief's  Desk. 

two  connecting  cords.  The  cord  circuit  should  embody,  among 
others,  the  features  which  are  peculiar  to  the  wire  chief's  equipment 
alone.  These  features  can  be  observed  by  referring  to  the  circuit 
shown  in  Fig.  84  and  comparing  the  plug  arrangement  at  each  end 
of  this  circuit  with  that  shown  in  the  testing  circuit  in  Fig.  81.  It 
will  be  noted  that  they  are  the  same,  that  is,  they  are  so  connected 
normally  that  they  can  be  inserted  into  the  line  jacks  without  dis- 
turbing the  line  continuity.  When  the  board  is  provided  with  audible 


1 86  TOLL  TELEPHONE  PRACTICE 

instead  of  visual  busy  signals,  this  arrangement  is  not  required,  be- 
cause the  wire  chief  can  test  the  line  before  plugging  in,  to  determine 
whether  or  not  it  is  busy. 

After  determining  that  the  line  is  idle,  the  wire  chief  will  operate 
keys  3  and  10,  which  will  connect  the  cords  at  each  end  of  the  circuit. 
This  connection  is  practically  the  same  as  a  connection  put  up  at 
the  toll  board  and  the  disconnect  signals  are  obtained  in  the  usual 
manner.  The  principal  use  for  a  circuit  of  this  kind  is  to  get  a  call 
through  from  the  line  to  the  toll  board,  when  the  line  circuit  between 
the  desk  and  the  board  is  out  of  order.  The  wire  chief  may  also  use 
this  circuit  for  talking  to  his  men  on  lines  which  have  been  plugged 
up  for  test. 

For  the  convenience  of  the  wire  chief  in  reaching  the  operators  at" 
the  toll  board,  or  the  chief  operator,  and  vice  versa,  it  is  customary 
to  provide  several  trunks  for  intercommunication;  a  very  satisfac- 
tory plan  is  to  multiple  the  inter-position  trunks  through  the  wire 
chief's  desk.  The  wire  chief's  telephone  set,  pilot  and  night  alarm 
circuits  are  essentially  the  same  as  those  used  at  the  standard  line 
position.  The  general  arrangement  of  apparatus  at  a  wire  chief's 
desk  can  be  readily  observed  from  the  two-position  desk  shown  in 
Fig.  85. 


CHAPTER  XII 
SIMPLEX   SYSTEMS 

THE  economy  of  a  wire  plant  which  results  from  the  ability  to 
transmit  telephone  and  telegraph  messages  simultaneously  over  a 
single  circuit  is  of  the  greatest  importance  commercially.  The  added 
cost  of  apparatus  in  systems  for  simultaneous  transmission  is  insignifi- 
cant compared  with  the  added  revenue.  Such  apparatus  has  been 
used  most  extensively  in  toll  systems,  in  which  the  derived  telegraph 
circuits  have  been  leased  largely  for  private  use. 

The  demand  in  this  country  for  private  telegraph  circuits,  or  leased 
lines  as  they  are  called,  is  considerable.  They  are  employed  by  stock 
and  grain  brokers  very  extensively  and  often  by  large  industrial  con- 
cerns who  have  offices  or  plants  at  different  localities.  They  are  also 
employed  by  the  wire  companies  themselves  for  the  transmission  of 
company  business  and  sometimes  as  an  aid  in  handling  toll  telephone 
traffic. 

There  are  two  systems  of  simultaneous  transmission  in  common 
use,  the  simplex  and  the  composite  systems.  The  simplex  system 
secures  the  transmission  of  one  telephone  message  and  one  telegraph 
message  over  one  pair  of  wires.  The  composite  system  secures  the 
transmission  of  one  telephone  message  and  two  telegraph  messages 
over  one  pair  of  wires.  The  former  is  virtually  a  phantom  circuit 
scheme,  but  the  latter  is  fundamentally  a  system  of  simultaneous 
transmission  over  the  same  wire  without  interference. 

Theory.  —  In  opening  the  discussion  of  the  simplex  system,  it  is 
considered  expedient  to  show  first  a  skeleton  circuit  illustrating  the 
theory  of  the  scheme  or  method.  This  circuit  is  shown  in  Fig.  86  and 
it  will  be  observed  readily  that  the  principle  taken  advantage  of  is 
that  of  the  wheats  tone  bridge  principle.  This  circuit  shows  only  the 
morse  equipment,  with  the  usual  apparatus  at  each  terminal.  Such 
telegraph  circuits,  as  will  be  noted,  take  the  place  of  the  battery  in 
the  wheats  tone  bridge,  while  coils  X,  Y,  X'  and  Yr  constitute  the 
four  arms  of  the  bridge.  Leads  a  and  b  are  the  line  wires  and  since 

187 


i88 


TOLL  TELEPHONE  PRACTICE 


for  all  practical  purposes  the  resistances  of  these  wires  can  be  kept 
so  nearly  alike  as  to  prevent  any  perceptible  unbalance,  a  galvanometer 
placed  as  shown  will  always  indicate  a  balanced  condition,  i.e.,  two 
points  on  the  line  wires  equally  distant  from  the  office  will  be  at  equal 
potential  and  consequently  no  current  will  flow  through  the  gal- 
vanometer. Therefore,  when  keys  K  and  K'  are  closed,  a  current 
will  flow  from  battery  Bf  through  the  key  contact  and  relay  R'  to  Z'; 


FIG.  86.  —  Theoretical  Diagram  of  a  Simplex  Circuit. 

at  this  point  the  current  divides,  half  of  it  traversing  the  upper  bridge 
arm  and  the  other  half  the  lower  arm,  to  the  point  Z,  at  which  junction 
the  currents  unite  and  flow  through  relay  R,  through  the  key  to 
battery  B  and  back  through  the  earth  to  battery  Bf.  The  path  of 
the  current  can  be  traced  readily  with  the  aid  of  the  arrows  in  the  figure. 
Repeating  Coil  Method.  —  These  conditions  may  be  embodied  in 
a  telephone  line  as  shown  in  Fig.  87,  which  represents  a  standard 
simplex  system  using  the  repeating  coil  method.  It  will  be  noted 
that  either  telephone  jack  is  wired  direct  to  one  winding  of  a  repeating 
coil,  the  opposite  winding  being  carried  to  the  line  wires ;  consequently 
the  telephone  talking  circuit  is  identical  with  that  ordinarily  used  in 
toll  work  in  connecting  grounded  lines  to  metallic  lines.  The  tele- 
graph circuit  is  connected  to  the  middle  points  of  windings  2  and  2' 
of  the  repeating  coils  A  and  A',  respectively;  and  thereby  the  balanced 
wheatstone  circuit  is  established.  The  toll  circuit  will  therefore  be 
balanced  at  all  times  as  regards  the  telegraph  current.  It  should  be 
noted  further  that  the  additional  resistance  inserted  into  the  telegraph 
circuit  due  to  the  windings  of  the  repeating  coils  is  quite  immaterial, 
since  the  two  line  wires  are  connected  in  parallel  and  consequently 


SIMPLEX  SYSTEMS 


189 


the  line  resistance  is  cut  in  two.  Furthermore,  since  the  telegraph 
•circuit  is  connected  to  the  middle  of  either  repeating  coil  winding,  the 
current  will  divide  equally  and  flow  from  the  center  toward  each  end ; 
thus  these  halves  of  the  coil  will  act  non-inductively,  since  the  mutual 
inductance  neutralizes  the  self -inductance.  It  will  be  observed  that 
each  telegraph  key  is  shunted  with  a  condenser,  the  object  of  which 
is  to  take  up  the  spark  at  the  key  contact.  This  naturally  saves  con- 


'I'I'I'I'N'I'hL 


FIG.  87.  —  Simplex  Circuit,  Using  a  Repeating  Coil. 

siderable  wear  and  tear  at  the  key  contacts.  It  might  be  well  to  state 
that  it  is  also  the  practice  in  some  cases  to  shunt  the  relay,  as  well  as 
the  key  contact,  with  this  condenser.  When  this  is  done,  however, 
it  makes  the  relay  action  sluggish,  although  it  reduces  to  a  greater 
extent  the  inductive  kick  on  the  line,  due  to  the  magnetic  energy 
stored  in  the  telegraphic  relay. 

The  paths  of  the  telephone  and  the  telegraph  currents  can  be  fol- 
lowed easily  in  Fig.  87,  by  means  of  the  arrows.  The  wavy  arrows 
indicate  the  telephone  current  and  the  straight  arrows  the  telegraph 
current. 

Retardation  Coil  Method.  —  There  is  another  method  by  which  the 
same  results  can  be  obtained  with  the  use  of  retardation  coils  in  place 
of  repeating  coils.  Fig.  88  shows  a  standard  simplex  circuit  utilizing 
the  retardation  coil  method.  These  coils  usually  contain  two  parallel 
windings  upon  a  very  heavy  iron  core.  The  core  is  made  of  soft 
iron  wire  which  is  either  bent  back  from  the  ends  of  the  coil  so  as  to 


igo 


TOLL  TELEPHONE  PRACTICE 


meet  in  the  middle  (on  the  outside) ,  thereby  making  a  closed  magnetic 
circuit,  or  the  wires  may  be  formed  into  a  ring.  The  latter  coil  is 
known  as  the  toroidal  type.  A  closed  magnetic  circuit  is  desirable  in 
order  to  give  a  maximum  impedance  and  a  minimum  shunting  effect 
on  telephonic  transmission. 

By  referring  to  the  figure  it  will  be  observed  that  the  telegraph 
circuit  is  tapped  from  the  middle  of  the  winding  of  the  retardation 


FIG.  88.  —  Simplex  Circuit,  Using  Retardation  Coils. 

coil  in  the  same  manner  that  this  circuit  was  attached  to  the  winding 
of  the  repeating  coil  in  the  previous  case;  the  coil  is  then  bridged 
directly  across  the  line.  The  telephone  circuit  is  protected  from  the 
telegraph  pulsations  by  the  condensers  placed  in  each  side  of  the  line. 
Since  a  fair  rate  of  speed  for  hand  sending  is  twenty-five  words  per 
minute,  which  would  mean  about  five  dots  and  spaces  per  second, 
the  condenser  impedance  will  be  very  high  and  will  greatly  dimmish 
the  impulses  passing  to  the  telephone  circuit.  However,  since  the 
average  frequency  of  telephone  currents  amounts  to  about  eight 
hundred  cycles  per  second,  these  condensers  will  then  offer  a  relatively 
low  impedance.  *The  retardation  coil,  on  the  other  hand,  offers  a  very 
great  impedance  to  such  a  frequency  and  thus  the  efficiency  of  tele- 
phone transmission  is  but  little  impaired.  The  paths  of  the  telephone 
and  the  telegraph  currents  in  this  circuit  can  be  followed  easily  by  the 
arrows,  the  notation  of  which  in  all  cases  will  be  the  same  as  that  used 
in  the  previous  case,  i.e.,  the  straight  arrow  for  telegraph  currents 
and  the  wavy  arrow  for  telephone  currents. 

There  are  advantages  to  be  claimed  for  either  of  the  above  systems 


SIMPLEX  SYSTEMS 


191 


and  the  most  important  of  these  may  be  enumerated  as  follows.  In 
the  first  place,  the  retardation  coil  system  is  cheaper  to  install  and 
the  efficiency  of  the  talking  circuit  is  not  reduced  to  the  extent  that 
it  is  in  the  repeating  coil  system,  with  the  repeating  coil  losses.  This 
is  due  to  the  fact  that  these  repeating  coils  must  be  designed  for 
transforming  both  voice  currents  and  ringing  currents,  and  consequently 
are  not  built  to  give  a  talking  efficiency  of  the  highest  obtainable  value. 
Therefore,  when  several  of  these  repeating  coils  are  placed  in  a  long 
circuit,  the  voice  transmission  is  very  materially  reduced.  In  the 
repeating  coil  system,  however,  no  trouble  is  experienced  in  ringing 
with  grounded  generators,  but  such  a  generator  used  in  connection 
with  the  retardation  coil  system  will  disturb  all  of  the  telegraph 
apparatus  on  the  line.  It  might  be  said  in  general,  that  the  repeating 
coil  system  is  best  adapted  to  short  lines,  while  the  retardation  coil 
system  may  be  used  for  lines  of  any  length  and  is  much  superior  for 
long  lines  with  several  intermediate  telegraph  stations. 

It  is  frequently  necessary  to  have  an  intermediate  telegraph  station 
where  no  telephone  connection  is  needed,  and  vice  versa.  The  simplex 
system  is  quite  flexible  in  this  respect  and  many  combinations  are 
easily  arranged. 

Fig.  89  shows  an  intermediate  telegraph  station  in  conjunction  with 
a  through  telephone  circuit;  and  several  such  stations  can  be  worked 


FIG.  89.  —  Diagram  of  an  Intermediate  Telegraph  Station  on  a  Simplex  Line. 

in  series  on  the  same  line.  The  general  principles  explained  in  con- 
nection with  the  circuit  of  Fig.  88,  as  regards  the  functions  of  capacity 
and  inductance,  are  applicable  in  this  case  also  and  need  not  be  re- 
peated. The  paths  of  the  currents  can  be  traced  easily  by  means  of 


192  TOLL  TELEPHONE  PRACTICE 

the  arrows.  Fig.  90  shows  a  through  telephone  circuit  and  two  termi- 
nal telegraph  stations;  that  is  to  say,  each  telegraph  station  operates 
independently  of  the  other,  while  the  telephone  circuit  is  continuous. 
The  principal  difference  between  this  and  the  circuit  immediately 


FIG.  90.  —  Diagram  of  a  Terminal  Telegraph  Station  on  a  Simplex  Line. 

preceding  is  that  in  Fig.  89  the  operation  of  the  telegraph  key  trans- 
mits the  signals  both  ways,  thereby  actuating  all  the  telegraph  instru- 
ments on  the  line;  while  in  Fig.  90  the  operation  of  the  telegraph  key 
sends  out  an  impulse  in  but  one  direction.  This  can  be  readily  seen 
by  following  the  arrows  in  the  figure. 

In  addition  to  the  intermediate  and  terminal  telegraph  station  there 
is  the  so-called  telephone  terminal  station,  which  is  illustrated  in 
Fig.  91.  This  figure  also  shows  the  American  Telephone  and  Tele- 
graph Company's  standard  repeater  circuit.  This  repeater  circuit 
is  used  in  long  telegraph  lines  to  boost  the  telegraph  current,  or  rather 
to  replace  the  distant  battery  by  a  new  one  at  an  intermediate  station, 
thus  working  the  long  circuit  in  two  or  more  parts,  each  part  being 
energized  by  a  distinctly  separate  set  of  batteries.  A  brief  description 
of  the  operation  of  this  repeater  next  follows. 

It  will  be  noted  that  the  telephone  connections  in  Fig.  91  are  derived 
in  the  usual  manner  and  that  the  telegraph  circuit  is  looped  through 
from  the  middle  of  repeating  coil  B,  through  the  telegraph  apparatus 
and  thence  to  the  middle  of  repeating  coil  Bf.  The  flow  of  the  currents 
may  be  traced  by  means  of  the  arrows. 

All  the  circuits  in  the  repeater  are  normally  closed  as  shown  in 


SIMPLEX  SYSTEMS 


193 


the  figure,  but  when  the  operator  at  the  distant  southern  station  opens 
his  key,  it  will  cause  the  release  of  relay  R'j  which  in  turn  will  de- 
energize  coil  V  of  the  telegraph  transmitter.  The  two  coils  H  and 
Ef  of  the  transmitter  are  normally  short-circuited  by  the  contacts 


FIG.  91.  —Terminal  Telephone  Station  and  Telegraph  Repeater. 

T  and  T'  of  the  transmitter  armatures.  Therefore,  when  coil  Vf  of 
the  transmitter  is  de-energized,  it  will  cause  the  armature  to  fall  back. 
This  armature  is  pivoted  at  X'  and  is  so  arranged  that  in  falling  back 
the  contact  at  Tr  is  broken  before  the  one  atZ'.  The  breaking  of  the 
contact  at  T'  removes  the  shunt  around  coil  H  and  thus  causes  a  flow 
of  current  through  this  coil  by  means  of  a  circuit  that  can  be  traced 
from  battery  A',  through  coil  N',  thence  by  way  of  contact  T,  coil  H, 
resistance  AT,  battery  A  and  finally  to  ground.  Consequently  the 
opening  of  the  circuit  containing  relay  R,  at  contact  Z',  will  not  release 
the  armature  of  the  other  transmitter.  Thus  each  make  and  break 
of  the  key  at  the  southern  station  will  cause  a  corresponding  make  and 
break  at  Z',  and  will  thereby  send  out  an  impulse  from  the  line  battery 
at  B,  over  the  north  end  of  the  line. 

In  case  the  operator  at  the  northern  station  desires  to  signal  the 
southern  operator  when  the  latter  is  sending,  the  former  need  only  to 
open  his  key  and  then  the  following  conditions  will  be  established. 
As  soon  as  the  contact  Z'  closes,  the  short  circuit  on  coil  H  will  be  re- 
established; but  the  circuit  through  relay  R  is  open  at  the  distant 


IQ4  TOLL  TELEPHONE  PRACTICE 

northern  station,  so  that  the  armature  of  the  transmitter  will  drop 
back  and  open  the  contact  T.  Thus  coil  E'  is  energized  and  will 
hold  up  its  armature.  The  operator  at  the  northern  end  is  now  in  a 
position  to  communicate  with  the  southern  operator  in  a  manner 
identical  with  that  just  described  for  sending  messages  in  the  opposite 
direction. 


CHAPTER  XIII 
COMPOSITE  SYSTEMS 

BY  the  method  of  simplexing  it  is  possible  to  transmit  a  telephone 
and  a  telegraph  message  over  one  pair  of  wires  simultaneously.  The 
economy  thus  obtained  is  well  worth  having,  but  with  the  composite 
system  it  is  possible  to  send  simultaneously  one  telephone  and  two 
telegraph  messages  on  the  same  pair  of  wires,  the  earth  being  used  as 
a  return  for  the  telegraph  circuits;  or  one  telephone  and  one  telegraph 
message  if  but  one  wire  is  used,  in  which  case  the  earth  is  used  as  a 
return  for  both  circuits.  Thus  it  is  possible,  by  the  last  method,  to 
operate  the  very  expensive  toll  lines  at  a  telegraph  efficiency  which  is 
100  per  cent  higher  than  that  obtained  by  simplexing;  consequently 
if  a  telephone  company  can  create  a  sufficient  demand  for  telegraph 
service,  there  is  an  opportunity  to  largely  increase  the  revenue  per 
mile  of  wire.  This  arises  from  the  fact  that  about  75  per  cent  of  the 
total  investment  is  in  poles,  cables,  conduits  and  wires  and,  therefore, 
any  additional  expenditure  on  the  terminal  plant  which  will  increase 
the  earning  power  of  the  outside  plant  is  a  very  profitable  investment. 

In  the  simplex  circuit  both  of  the  telephone  wires  are  operated  in 
parallel  for  the  telegraph  or  morse  circuit,  while  in  a  composite  sys- 
tem each  line  conductor  constitutes  a  separate  morse  circuit.  Con- 
sequently, with  the  composite  system,  mutual  interferences  between 
the  telephone  and  the  telegraph  operation  must  be  guarded  against; 
and  then  there  is  the  additional  complication  of  possible  interference 
between  the  two  telegraph  circuits,  which  is  commonly  known  as 
"  cross  writing."  There  are  several  practical  methods  of  compositing 
a  telephone  line,  but  the  following  method  has  been  used  with  great 
success  by  the  American  Telephone  and  Telegraph  Company.  Fig. 
92  shows  an  ordinary  grounded  telephone  circuit  composited  for 
telegraphic  service. 

Grounded  Composite  System.  —  The  retardation  coils  A  and  A' 
each  consist  of  two  windings  whose  total  resistance  is  50  ohms;  they 
are  wound  on  very  heavy  soft  iron  cores  of  the  closed  type.  A  coil  of 

195 


196 


TOLL  TELEPHONE  PRACTICE 


COMPOSITE   SYSTEMS  197 

this  kind  as  used  by  the  American  Telephone  and  Telegraph  Company 
is  shown  in  Fig.  93.  These  windings  are  connected  differentially,  as 
shown  in  the  circuit,  and  the  action  of  such  a  coil  is  as  follows:  The 
direct  or  pulsating  current  of  a  low  fre- 
quency, such  as  that  produced  by  the 
manual  operation  of  a  telegraph  key,  the 
coil  acts  much  like  a  non-inductive  resist- 
ance, since  the  inductance  set  up  in  one- 
half  of  the  coil  is  largely  counteracted  by 
that  of  the  other  half.  However,  with  the 
high-frequency  voice  currents,  the  com- 
paratively small  inductance  gives  rise  to  a  FlG-  93-  —  Retardation  Coil 
very  large  impedance,  so  that  such  cur- 
rents scarcely  penetrate  the  coils  at  all.  This  type  of  coil  was  devel- 
oped experimentally  and  found  to  give  satisfactory  results,  which  seems 
to  be  the  main  reason  for  its  use.  There  seems  to  be  no  satisfactory 
explanation  from  a  theoretical  standpoint  for  the  adoption  of  this 
particular  design.  Coils  I  and  /'  are  also  composed  of  two  windings 
and  their  total  resistance  is  30  ohms.  These  windings  are  likewise 
placed  on  a  massive  soft  iron  core  of  the  closed  type,  but  are  connected 
in  series,  i.e.  the  windings  magnetize  the  core  in  the  same  direction; 
and  hence  such  a  coil  has  a  very  large  inductance.  Since  the  remainder 
of  the  apparatus  in  the  circuit  is  not  of  special  design,  we  may  now 
consider  the  operation  of  the  circuit  as  a  whole.  In  order  that  this 
description  may  be  as  simple  as  possible,  the  telegraph  circuit  will  be 
traced  first. 

The  operation  of  writing  at  key  K  will  send  a  pulsating  current  out 
on  the  line  by  way  of  relay  R  to  the  point  X.  At  this  junction,  part 
of  the  current  is  required  to  charge  the  condenser  C  and  the  remainder 
traverses  the  coil  A  to  the  point  Y.  However,  the  joint  action  of 
condenser  C  and  coil  A  on  the  telegraph  current  brings  about  very 
beneficial  results,  i.e.  the  otherwise  abrupt  changes  in  current  and 
potential  caused  by  the  actuation  of  the  telegraph  key  are  made  to 
take  place  more  slowly.  The  current  and  potential  here  meant  are 
those  of  the  line,  beyond  the  point  Y.  Fig.  94  shows  the  transforma- 
tion of  the  rectangular  wave  of  current  when  acted  upon  by  capacity 
and  inductances  as  explained.  This  action  may  be  explained  as 
follows :  The  depression  of  the  key  causes  a  heavy  flow  of  current  to 
the  point  X,  where  the  coil  A  acts  as  a  momentary  barrier,  and  mean- 


198  TOLL  TELEPHONE  PRACTICE 

while  the  condenser  C  will  be  charged;  upon  the  opening  of  the  key, 
the  condenser  C  tends  to  discharge  in  the  direction  of  the  original 
current  and  to  oppose  the  discharge  from  the  line,  thereby  tending  to 
maintain  the  flow  of  current  and  thus  causing  a  more  gradual  decrease. 
Hence  the  combined  action  of  the  coil  and  the  condenser  prevents  any 


FIG.  94.  —  Wave  Form  of  Telegraph  Current  in  Composite  Circuit. 

very  abrupt  fluctuation  of  current  in  the  line.  The  telegraph  current 
has  been  traced  to  the  point  Y  and  from  there  it  passes  to  the  line. 
At  the  distant  terminal  it  takes  a  similar  path  and  actuates  the  relay 
Rf.  Should  any  of  the  telegraph  current  leak  through  condenser  B, 
no  material  portion  of  it  will  reach  the  telephone,  because  the  shunt 
path  to  ground  through  the  coil  /  offers  relatively  much  less  impedance 
than  the  condensers  D  and  E. 

Turning  now  to  the  telephone  circuit,  it  is  evident  that  the  high- 
frequency  voice  currents  will  readily  pass  through  the  condensers  E, 
D  and  B,  and  will  be  choked  out  of  the  telegraph  circuit  by  means 
of  the  impedance  coil  A.  The  current  will  consequently  flow  over 
the  line  to  F',  where  it  is  again  choked  out  of  the  telegraph  circuit 
by  coil  A'  and  will  find  a  ready  path  through  condensers  E'  and  D' ', 
the  telephone  instrument  and  condenser  E'  to  ground.  Thus  the 
telephone  current  is  kept  out  of  the  morse  leg,  and  the  telegraph 
current,  in  its  turn,  cannot  interfere  with  the  telephone  circuit.  The 
paths  of  the  telephone  and  the  telegraph  currents  can  be  readily  traced 
by  means  of  the  arrows  in  the  figure. 

Metallic  Composite  System.  —  The  principles  made  use  of  in  com- 
positing a  grounded  line,  as  explained  above,  are  all  applicable  to  the 
problem  of  compositing  a  metallic  line,  but  in  the  latter  case  the 
possibility  of  cross  writing  must  be  carefully  guarded  against.  The 
circuit  of  a  composited  metallic  line  is  shown  in  Fig.  95.  The  arrange- 
ment of  apparatus  is  very  similar  to  that  shown  in  Fig.  92.  Since  the 
apparatus,  such  as  the  retardation  coils  A  and  /,  is  identical  with  that 


COMPOSITE  SYSTEMS 


199 


200  TOLL  TELEPHONE  PRACTICE 

previously  described,  it  is  possible  to  start  immediately  with  a  narrative 
of  the  operation  of  the  circuit.  When  the  key  K  is  actuated,  a  pul- 
sating current  will  flow,  as  previously  described,  through  relay  R  and 
coil  A  out  on  the  telegraph  line,  and  thence  by  way  of  coil  Af  and 
relay  R'  to  battery.  The  functions  of  condensers  C,  B,  D  and  E 
and  coils  A  and  7  are  identical  with  those  described  for  the  grounded 
circuit.  However,  in  this  case  there  are  two  morse  wires  and  these 
are  interconnected  through  each  telephone  drop.  In  sending  on  either 
morse  circuit,  slight  impulses  will  pass  through  the  drop  or  the  tele- 
phone to  the  opposite  morse  circuit  unless  means  to  prevent  this  are 
provided.  The  function  of  the  coils  7  and  7'  is  to  minimize  or  prevent 
this  cross  writing,  by  providing  shunt  paths  to  ground  for  these 
impulses.  The  operation  of  the  telephone  circuit  is  practically  the 
same  as  that  described  for  the  grounded  system,  the  ground  return 
being  replaced  by  the  second  morse  wire.  In  passing  it  might  be  well 
to  add  that  for  the  most  satisfactory  operation  of  the  telephone  circuit, 
the  condensers  B,  B',  N  and  N'  should  be  limited  in  their  capacity, 
four  microfarads  as  indicated  in  the  circuits  shown  in  Figs.  92  and  95 
giving  very  satisfactory  results.  Although  it  is  a  well-established  fact 
that  as  the  capacity  of  a  condenser  is  increased,  the  efficiency  with 
which  it  will  transmit  voice  current  is  likewise  enhanced,  the  limit  to 
which  the  capacity  of  these  condensers  may  be  raised  is  soon  reached. 
This  is  due  to  the  fact  that,  as  the  potential  of  the  telegraph  line  rises 
and  falls  with  the  make  and  break  of  the  telegraph  key,  a  very  notice- 
able disturbance  will  be  created  in  the  telephone  circuit  by  the  greater 
charging  currents  in  the  condensers.  There  is  a  circuit  in  use  giving 
very  satisfactory  results,  in  which  the  condensers  D  and  E  have  been 
entirely  omitted;  in  this  case  the  capacity  of  B  is  reduced  to  two 
microfarads.  The  capacity  of  condenser  C  varies  from  six  to  twelve 
microfarads. 

The  most  serious  objection  to  the  composite  circuit  arises  from  the 
fact  that  it  contains  so  much  capacity  to  ground.  These  condensers 
must  be  fully  charged  before  the  telegraph  current  on  the  line  can 
attain  its  maximum  value;  and  hence  the  telegraph  relay  will  not 
respond  instantly  to  the  touch  of  the  key.  This  condition  is  rather 
detrimental  when  very  fast  sending  is  being  done,  but  for  ordinary 
work  the  operation  of  the  circuit  is  quite  satisfactory. 

Composite  Ringer.  —  An  apparent  objection  to  this  system  arises 
from  the  fact  that  the  ordinary  telephone,  generator  cannot  be  used 


COMPOSITE  SYSTEMS 


201 


2O2 


TOLL  TELEPHONE  PRACTICE 


for  signaling,  because  the  frequency  of  the  ringing  current  is  low 
enough  to  find  a  path  through  the  coils  A,  Af,  Z  and  Z'  and  thus  cause 
the  telegraph  relays  to  chatter.  This  difficulty  is  avoided  by  a  special 
composite  ringer  which  is  shown  in  Fig.  96.  In  this  circuit  the  tele- 
graph apparatus  for  each  morse  wire  and  all  the  necessary  telephone 
equipment  is  shown,  but  the  description  will  be  limited  to  the  operation 
of  the  ringing  mechanism.  In  this  circuit  there  are  several  pieces  of 
apparatus  of  special  design  which  require  description  before  the  opera- 
tion of  the  circuit  can  be  understood. 

Relay  L  is  so  designed  that  it  will  be  actuated  by  an  alternating 
current  of  low  frequency  such  as  that  generated  by  the  ordinary 
ringing  dynamotor.  The  construction  of  this  relay  is  shown  in  Fig.  97. 


FIG.  97.  —  Low-frequency  Alternating-current  Relay. 

This  drawing  shows  the  top  and  side  views  of  the  relay.  It  will  be 
noted  that  the  armature  is  very  massive  and  heavy,  and  its  inertia  is 
sufficient  to  hold  it  in  place  when  once  attracted,  even  though  the 
magnetizing  current  is  alternating  and  of  low  frequency.  The  contact 
springs  are  long  and  very  flexible,  and  although  the  armature  has  a 
tendency  to  vibrate  slightly,  the  resiliency  of  the  springs  will  prevent 
the  opening  of  the  local  contacts.  The  break  contact  is  held  in  place 
by  the  weight  of  the  armature;  a  rubber  bushing  imbedded  in  the 
armature  normally  rests  upon  the  upper  spring  of  this  pair  of  contacts. 
The  make  contact  is  actuated  when  the  armature  is  drawn  up,  due 
to  the  fact  that  the  insulated  tip  of  set-screw  C  forces  spring  A  into 
contact  with  B.  The  magnetic  circuit  of  the  relay  can  be  traced  from 
the  core  of  the  coil,  through  the  armature  and  thence  through  the  two 
metallic  sides  D  and  E,  to  the  front  of  the  core.  Therefore,  as  soon 
as  sufficient  magnetic  energy  is  set  up  in  the  core  of  the  coil,  the  arma- 


COMPOSITE   SYSTEMS 


203 


ture  will  be  raised  to  a  horizontal  position,  reducing  the  air  gap  to  a 
minimum. 

Another  piece  of  ingenious  apparatus  is  the  high-frequency  alter- 
nating-current relay  Q,  which  is  designed  with  a  small  inertia  of  the 
moving  parts,  so  as  to  respond  to  comparatively  weak  alternating 
currents  of  high  frequency.  This  relay  is  shown  in  Fig.  98.  The 


FIG.  98.  —  High-frequency  Alternating-current  Relay. 

design  is  a  radical  departure  from  ordinary  methods,  and  the  prin- 
ciple upon  which  it  operates  is  similar  to  that  of  a  polarized  bell. 
The  permanent  magnet  A  energizes  the  cross  piece  D,  thereby  pro- 
ducing a  pole  of  the  same  polarity  as  that  of  A  in  the  cores  of  coils 
B  and  B',  by  means  of  the  paths  through  the  supports  G  and  G'.  At 
the  other  end  of  the  magnet  A  the  reed  F  is  magnetized  through  the 
support  H,  and  hence  the  polarity  of  the  reed  at  the  coil  end  will  be 
opposite  to  the  induced  polarity  in  the  cores  before  mentioned.  The 
reed  is  adjusted  with  a  slight  normal  bias  to  give  a  firm  closure  of  its 
local  contacts.  The  coils  B  and  Bf  are  so  connected  that  they  pro- 
duce magnetic  poles  of  opposite  polarity.  It  follows  that  an  alter- 
nating current  during  a  given  half  cycle  will  strengthen  one  pole  while 
it  weakens  the  other  and  during  the  next  half  cycle  will  reverse  its 
effect.  The  resultant  field  will  cause  the  reed  to  vibrate  synchro- 
nously. This  reed  F  is  a  stiff  steel  spring  whose  natural  period  of 
vibration  is  relatively  high.  Directly  above  this  reed  is  another  reed 
C  of  light  non-magnetic  material,  which  makes  contact  with  reed  F 
at  point  Z.  The  operation  of  the  relay  may  now  be  explained  as 


204  TOLL  TELEPHONE  PRACTICE 

follows:  When  an  alternating  current  of  high  frequency  traverses 
the  coils  B  and  Bf,  the  reed  F  is  set  into  synchronous  vibration;  in 
its  movement  it  will  strike  reed  C,  whose  action  is  comparatively 
slow.  The  rate  of  vibration  of  reed  C  is  retarded  by  the  lead  weight 
X  which  is  placed  at  the  contact  end  of  the  reed.  Under  these  con- 
ditions the  contact  Z  is  closed  but  a  very  small  fraction  of  the  time 
and  for  all  practical  purposes  is  open.  The  adjustment  of  the  relay  is 
accomplished  by  means  of  thumbscrew  E  and  the  associated  spring, 
which  control  reed  C. 

When  the  toll  operator  wishes  to  ring  over  the  line  her  procedure 
is  not  different  from  ordinary  ringing,  which  is  already  very  familiar. 
The  usual  operation  causes  the  low-frequency  ringing  current  to  flow 
out  over  the  tip  of  the  jack  to  the  armature  of  relay  T  and  thence  by 
means  of  the  break  contact  i  to  the  tip  of  the  line,  condenser  F,  the 
coil  of  relay  L  and  the  ring  of  the  line  to  the  break  contact  2  of  relay 
T  and  back  to  the  ring  of  the  jack.  No  appreciable  portion  of  this 
current  will  flow  through  the  shunt  path  offered  by  condenser  G  and 
the  high-frequency  relay  Q,  since  this  condenser  has  a  capacity  of 
only  one-half  microfarad  and  therefore  offers  a  very  high  impedance 
at  the  ringing  frequency.  Due  to  the  completion  of  the  circuit  just 
outlined  the  slow-acting  alternating-current  relay  L  will  be  actuated. 
The  attraction  of  armature  i  will  open  the  shunt  path  around  relay 
L  through  the  high-frequency  relay  and,  consequently,  the  small 
component  which  flows  through  the  shunt  circuit  will  exist  only 
momentarily.  The  attraction  of  armature  2  of  relay  L  will  complete 
a  circuit  which  may  be  traced  as  follows:  from  the  ground  on  arma- 
ture 2  of  this  relay,  by  way  of  the  make  contact,  to  the  coil  of 
relay  K  and  thence  through  the  coil  of  relay  U  to  battery.  Thus 
relays  K  and  U  will  be  energized.  The  attraction  of  the  armature 
of  relay  U  will  close  the  following  circuit:  from  the  ringing  dyna- 
motor  to  the  armature  of  the  same  relay  and  thence  by  way  of  the 
make  contact  to  the  make  contact  and  the  armature  of  the  high- 
frequency  vibrator  F,  through  the  coils  of  the  latter  and  then  by  way  t 
of  the  primary  of  the  transformer  back  to  the  generator.  The  com- 
pletion of  this  circuit  will  energize  the  coils  of  the  high-frequency 
vibrator,  which  is  self  interrupting. 

It  will  be  noted  from  the  above  description  that  the  high-frequency 
vibrator  is  in  fact  nothing  more  or  less  than  a  buzzer-like  contrivance 
for  furnishing  a  current  of  such  high  frequency  and  small  amplitude 


COMPOSITE   SYSTEMS  205 

that  it  will  not  affect  the  telegraph  instruments.  It  will  be  further 
observed  that  the  armature  and  make  contact  of  the  vibrator  are 
shunted  by  a  noninductive  resistance  of  1000  ohms,  the  object  of 
which  is  to  reduce  sparking  at  the  contacts.  This  resistance  is  pur- 
posely made  so  high  that  the  vibrator  armature  will  release  freely. 
The  vibrator  is  designed  to  furnish  about  twenty  interruptions  or 
cycles  for  each  cycle  of  the  ordinary  ringing  current.  Thus  the  fre- 
quency is  in  the  vicinity  of  300  cycles  per  second  and  will  not  interfere 
with  the  operation  of  the  telegraph  apparatus  on  a  composited  line. 
The  function  of  the  condenser  H  is  to  increase  the  amplitude  of  the 
secondary  E.M.F.,  which  it  does  by  facilitating  the  discharge  of  the 
magnetic  energy  of  the  vibrator  and  the  primary  of  the  transformer. 
It  will  be  obvious  that  as  long  as  relay  U  is  actuated,  the  vibrator 
will  establish  a  pulsating  current  of  high  frequency,  which  traverses 
the  primary  winding  of  the  transformer.  Consequently  there  will  be 
induced  in  the  secondary  an  alternating  current  of  a  like  frequency, 
which  will  find  its  way  to  the  line  by  means  of  the  following  path: 
from  the  transformer  to  the  make  contact  of  armature  i  of  relay  K, 
which  has  been  previously  operated  as  stated  above;  and  thence  by 
way  of  this  armature  through  condensers  D  and  B  to  the  tip  of  the 
line,  returning  by  way  of  the  ring  of  the  line  to  condensers  N  and  E, 
armature  2  and  the  make  contact  of  relay  K  and  then  to  the  trans- 
former. Since  this  current  is  of  high  frequency  it  will  meet  excessive 
impedance  from  coils  A  and  Z  or  /  and  W  and,  consequently,  will  not 
interfere  with  the  telegraph  instruments. 

An  incoming  high-frequency  signal  arriving  over  the  tip  side  of  the 
line  will  pass  through  condensers  B  and  D  to  armature  i  and  the  break 
contact  of  relay  K,  thence  by  way  of  condensers  F  and  G  to  the  coils 
of  the  high-frequency  relay  Q,  then  to  the  break  contact  of  relay  L 
and  thence  by  way  of  armature  2  of  relay  K,  through  condensers  E 
and  N  and  back  to  the  ring  side  of  the  line.  The  current  will  pass 
mainly  through  the  high-frequency  relay  on  account  of  the  relatively 
large  impedance  of  the  relay  Z,  and  the  small  component  which  trav- 
erses the  latter  will  be  insufficient  to  actuate  it.  The  actuation  of 
relay  Q  will  open  the  circuit  containing  relay  S,  and  hence  the  latter 
will  be  de-energized.  Since  relay  5  is  slow-acting,  any  momentary 
closure  of  the  contacts  of  the  high-frequency  relay  will  be  without 
effect.  The  release  of  relay  5  will  close  a  circuit  from  the  ground  on 
its  armature  to  its  break  contact  and  thence  to  relay  T  and  battery. 


206  TOLL  TELEPHONE  PRACTICE 

Thus  relay  T  will  be  energized  and  will  thereby  complete  the  follow- 
ing circuit;  from  the  ringing  generator  to  the  make  contact  of  arma- 
ture i,  then  by  way  of  the  armature  to  the  tip  of  the  jack  and  its 
break  contact,  through  the  coil  of  the  line  drop,  thence  to  the  other 
break  contact  and  the  ring  of  the  jack,  to  armature  2  and  the  make 
contact  of  relay  T  and  back  to  the  generator.  Thus  the  regular 
ringing  current  will  traverse  the  coil  of  the  drop  and  actuate  it  in  the 
usual  manner.  The  line  is  cut  off  at  the  break  contacts  of  relay  T 
and  hence  the  ringing  current  from  the  generator  cannot  affect  the 
morse  apparatus. 

Railway  Composite  System.  —  The  railway  composite  is  a  special 
development  of  the  .general  system  designed  to  meet  the  conditions 
on  railway  telegraph  lines.  It  is  now  quite  extensively  employed  by 
the  railway  systems  over  the  country,  particularly  in  the  West. 

Reference  to  the  circuit  in  Fig.  99  shows  that  the  telephone  circuit 
terminates  in  a  subscriber's  set  instead  of  a  jack  as  in  the  systems 
previously  explained.  This  set  contains  all  the  apparatus  required 
for  a  telephone  terminal,  therefore  the  work  of  installing  a  telephone 
set  in  this  type  of  line  consists  in  merely  stringing  a  lead  from 
the  line  wire  to  the  instrument.  The  simplicity  of  this  installation 
is  one  of  the  advantages  of  the  system  and  is  often  made  use  of 
for  emergency  service.  The  distance  intervening  between  telegraph 
stations  on  the  western  railroad  lines  is  often  very  great  and,  if  a 
train  were  to  be  stalled  or  wrecked  midway  between  two  of  these 
stations,  it  would  therefore  take  some  time  for  a  man  to  walk  to  the 
nearest  station  to  secure  assistance.  However,  if  the  train  is  equipped 
with  a  portable  emergency  set,  the  message  can  be  readily  sent  at 
once,  since  the  train  crew  can  tap  the  wire  and  report  by  means 
of  the  telephone;  thus  the  loss  of  much  valuable  time  and  many 
serious  delays  may  be  avoided.  These  instruments  when  arranged 
for  train  service  are  provided  with  a  pole,  one  end  of  which  terminates 
in  a  metallic  hook  for  engaging  the  line  wire.  The  rails  usually  serve 
for  the  ground  connection.  The  telephone  instrument  is  nothing 
more  than  an  ordinary  local  battery  set  equipped  with  a  special 
induction  coil,  which  is  utilized  both  in  speech  transmission  and  in 
the  generating  of  the  signaling  current.  The  set  is  not  equipped 
with  a  ringer,  this  being  replaced  by  a  special  signaling  device  H, 
as  shown  in  the  circuit  in  Fig.  99.  The  howler  H  used  in  this  circuit 
is  specially  designed  for  the  purpose,  the  diaphragm  being  made  of 


COMPOSITE   SYSTEMS 


207 


208  TOLL  TELEPHONE  PRACTICE 

heavier  stock  than  that  in  the  ordinary  receiver;  consequently  it  is 
not  distorted  or  weakened  by  the  rapid  vibration  of  comparatively 
large  amplitude,  to  which  it  is  subjected. 

The  combination  of  condenser  F  and  coil  Z  will  modify  the  telegraph 
impulses  as  described  previously.  The  telegraph  current  will  flow 
over  the  line  wire  until  it  reaches  an  intermediate  telegraph  station, 
such  as  that  shown  in  the  circuit;  at  this  point  it  has  three  paths,  one 
by  way  of  relay  D,  another  by  way  of  the  i  coo-ohm  noninductive 
resistance  B,  and  the  third  by  way  of  condenser  A.  However,  since 
the  telegraph  current  is  pulsating  in  nature,  it  will  not  flow  continu- 
ously through  condenser  A,  but  will  rather  select  the  paths  offered  by 
resistance  B  and  relay  D.  Since  the  resistance  coil  B  is  wound  to 
i ooo  ohms  and  the  morse  relay  D  is  but  150  ohms,  the  great  majority 
of  the  current  will  traverse  the  coil  of  the  relay  and  then  pass  out  on 
the  line  again.  The  function  of  resistance  B  is  to  prevent  response 
of  the  relay  to  the  telephone  ringing  current.  Condenser  A  retains 
the  continuity  of  the  telephone  circuit  when  the  telegraph  operator 
at  key  L  is  sending.  Any  telegraphic  line  current  consequently  will 
operate  the  telegraph  relay  D  and  all  other  intermediate  telegraph 
relays  in  the  line,  and  will  then  pass  through  coil  Z'  and  relay  R'  at 
the  other  end  of  the  line  and  thence  to  battery  and  ground.  The 
operation  of  any  telegraph  key  consequently  will  actuate  all  the  tele- 
graph relays  in  the  line  and  will  not  interfere  with  the  telephone 
circuit  because  the  telegraph  current  is  kept  out  of  the  instruments 
by  means  of  condensers  G  and  Gf. 

It  remains  to  be  explained  how  the  telephone  talking  and  ringing 
currents  are  transmitted  without  interfering  with  the  telegraph  cir- 
cuit. It  will  be  noted  that  the  telephone  sets  are  wired  in  multiple 
from  line  to  ground,  and  therefore  when  signaling  current  is  sent  out 
on  the  line,  all  the  telephone  instruments  will  respond.  When  there 
are  three  or  more  telephone  stations  a  system  of  code  ringing  must 
be  employed.  Fig.  99  shows  but  two  telephone  stations  and  one 
intermediate  telegraph  station,  but  the  number  of  intermediate 
stations  may  be  several,  depending  on  the  length  and  character  of 
the  circuit.  Ordinarily  four  or  five  telephone  stations  is  the  working 
limit. 

The  operation  of  the  telephone  circuit  is  as  follows:  When  a  train- 
man at  station  i  desires  to  call  another  telephone  station,  he  will 
actuate  key  K  the  required  number  of  times  to  give  the  proper  code 


COMPOSITE  SYSTEMS  2OQ 

ring,  with  the  following  results.  In  the  first  place  a  circuit  is  completed 
that  is  traceable  as  follows:  from  the  battery  to  the  primary  of  the 
induction  coil,  thence  to  the  armature  of  the  coil,  through  the  break 
contact  to  contact  i  of  key  K,  then  to  the  lever  spring  of  the  key  and 
back  to  the  other  side  of  the  battery.  This  induction  coil  is  similar 
to  the  standard  coil  in  a  subscriber's  local  battery  set,  with  the  extra 
feature  of  an  armature  and  a  break  contact.  Thus  when  the  above 

0 

circuit  is  completed  the  primary  of  the  coil  will  be  energized  and  will, 
therefore,  attract  the  armature  and  subsequently  break  the  circuit. 
This  will  release  the  armature  and  thus  close  the  circuit  again,  thereby 
energizing  the  primary  of  the  coil  and  causing  the  re-attraction  of  its 
armature,  which  will  be  repeated  indefinitely.  Thus  the  operation 
of  this  circuit  is  identical  with  that  of  an  ordinary  buzzer  or  vibrating 
bell.  The  making  and  breaking  of  the  primary  circuit  generates  an 
alternating  E.M.F.  in  the  secondary  which  is  impressed  on  the  line 
and  establishes  the  signaling  current.  This  alternating  current  will 
follow  a  path  which  can  be  traced  from  the  ground  on  the  switch  hook 
to  the  break  contact  of  the  latter,  then  to  the  lever  spring  of  key  K 
and  thence  by  means  of  contact  2  through  the  secondary  of  the  in- 
duction coil  and  condenser  G  out  on  the  line.  Due  to  the  large  in- 
ductance of  coil  Z  the  current  will  pass  almost  wholly  out  on  the  line, 
to  the  point  V.  At  this  junction  it  will  divide  among  the  three 
parallel  paths  as  offered  by  the  relay  R,  the  non-inductive  resistance 
B  and  the  condenser  A.  The  condenser  offers  the  least  impedance 
of  these  three  paths  and  therefore  conducts  a  large  fraction  of  the 
current.  The  portion  which  traverses  the  relay  D  is  too  small  to 
affect  its  armature.  The  signaling  current,  upon  leaving  the  inter- 
mediate telegraph  station  flows  over  the  line  to  condenser  G'  and 
thence  by  way  of  the  howler  H',  the  break  contact  of  key  K,  its  lever 
spring,  and  the  break  contact  of  the  hook  switch  itself,  to  ground. 
Thus  the  howler  will  be  energized  and  will  consequently  emit  the  code 
signal  imparted  to  the  key  K. 

The  removal  of  the  receiver  from  the  hook  will  close  the  primary 
circuit,  which  can  be  traced  from  the  battery  through  the  primary 
of  the  induction  coil  and  thence  by  way  of  the  transmitter  and  the 
hook  switch  to  contact  i  and  the  other  side  of  the  battery,  while  the 
secondary  circuit  can  be  traced  from  ground  by  way  of-  the  hook 
switch,  the  contact  2,  the  receiver,  the  secondary  of  the  induction 
coil  and  the  condenser  G  to  the  line.  Since  the  circuit  conditions  in 


210  TOLL  TELEPHONE  PRACTICE 

the  other  set  are  identical  with  those  just  described  at  station  i,  it  is 
plain  that  the  talking  circuit  is  complete;  and  since  the  frequencies  of 
talking  current  are  always  high,  the  path  followed  is  substantially  the 
same  as  that  given  for  the  signaling  current. 

The  telephone  circuit  employs  a  ground  return  and  is  naturally 
susceptible  to  the  noises  inherent  in  all  grounded  systems.  The 
induction  from  parallel  telegraph  circuits  is  sometimes  very  severe, 
but  all  such  disturbances  are  ordinarily  overcome  by  reducing  the 
sensitiveness  of  the  receivers.  On  this  account  it  is  seldom  possible 
to  secure  satisfactory  operation  over  a  circuit  of  more  than  one  hun- 
dred miles.  At  the  same  time  the  transmitters  must  be  made  as 
powerful  as  possible  and,  consequently,  the  number  of  cells  in  the 
primary  circuit  is  increased  to  seven  or  eight. 


CHAPTER  XIV 

PHANTOM   LINES 

0- 

IT  was  shown  in  the  last  chapter  that  the  efficiency  of  a  toll  wire 
plant  may  be  greatly  increased  by  employing  apparatus  which  per- 
mits simultaneous  use  of -the  same  wires  for  telephony  and  telegraphy. 
The  efficiency  may  be  still  further  increased  by  the  use  of  the  phantom 
circuit  principle.  Fig.  100  shows  how  four  retardation  coils  may  be 


FIG.  ioo.  —  Retardation  Coil  Type  of  Phantom  Circuit. 

inserted  in  two  metallic  circuits  so  as  to  obtain  an  additional  telephone 
circuit.  In  this  case,  the  two  standard  telephone  circuits  A  and  B 
are  called  the  physical  circuits,  while  circuit  C  is  termed  the  phantom 
circuit.  The  retardation  coils  are,  as  will  be  observed,  bridged  directly 
across  the  line  and  the  taps  for  the  phantom  circuit  are  taken  from 
the  middle  points  of  these  coils.  Thus  the  two  line  wires  of  each  of 
the  physical  circuits  are  operated  in  parallel  for  the  limbs  of  the 


212 


TOLL  TELEPHONE  PRACTICE 


phantom  circuit,  whose  line  resistance  is  consequently  but  half  as 
great  as  that  of  the  physical  circuits.  The  condensers  D,  E,  F,  G, 
etc.,  as  will  be  observed,  are  inserted  in  the  line  on  the  switchboard 
side  of  the  retardation  coils  and  usually  have  a  capacity  of  about 
four  microfarads.  These  condensers  are  not  necessary  for  the  satis- 
factory operation  of  the  phantom  and  are  only  used  in  this  connection 
so  that  the  physical  circuits  may  be  used  for  simplexing  when  phan- 
tom work  is  not  desired.  In  this  case  they  serve  to  keep  the  telegraph 
currents  out  of  the  switchboard  circuit.  The  ringing  and  the  talking 
currents  from  the  phantom  circuit  pass  readily  through  the  retarda- 
tion coils,  since  the  telephone  taps  are  taken  from  the  centers;  there- 
fore the  self-inductance  of  such  a  coil  is  neutralized  by  the  mutual 
inductance,  and  the  coil  as  a  whole  acts  like  a  noninductive  resist- 
ance. However,  to  an  alternating  current  flowing  in  circuits  A 
or  B,  these  coils  offer  their  full  inductance  and  a  correspondingly 
high  impedance.  Thus  it  is  obvious  that  signaling  or  talking  is  per- 
missible on  the  three  circuits  simultaneously,  without  any  mutual 
interference. 

In  this  connection  it  should  be  said,  however,  that  for  the  successful 
operation  of  a  phantom  circuit  the  physical  lines  should  be  extremely 


PHY6ICAL    CKT. 


•PHANTOM    CKT 


FIG.  101.  —  Repeating  Coil  Type  of  Grounded  Phantom  Circuit. 

well  balanced.  This  is  true  not  only  of  the  resistance,  but  likewise 
of  the  inductance,  the  capacity  and  the  leakage.  The  distribution  of 
potential  and  current  in  a  telephone  circuit  depends  upon  all  four  of 
these  properties  and  hence  they  must  all  be  considered  in  securing 
a  perfect  balance. 

Fig.  101  shows  a  grounded  phantom  circuit  employing  repeating 


PHANTOM   LINES 


2I3 


coils.  This  is  not  necessary,  however,  and  retardation  coils  may  be 
used  as  before,  if  desired.  The  ground  is  used  as  a  return  conductor 
for  the  phantom  circuit,  which  is  therefore  likely  to  be  noisy.  The 
switchboard  end  of  the  physical 
circuit  is  inductively  connected  to 
the  line  by  means  of  the  repeating 
coil  and  the  phantom  tap  is  taken 
from  the  middle  point  of  the  line 
winding  of  this  coil.  This  winding 
consequently  acts  as  a  noninduc- 
tive  resistance  in  the  phantom  cir- 
cuit, as  did  the  retardation  coil  in 
the  circuit  previously  explained; 
and  since  the  physical  circuit  makes  use  of  the  coil  as  a  simple  repeat- 
ing coil,  there  will  be  no  interference  between  the  two  circuits.  The 
one  objection  to  the  repeating  coil  method  is  that  these  coils  must 
be  designed  for  transmitting  both  ringing  and  talking  currents ;  hence 
the  efficiency  of  speech  transmission  is  somewhat  impaired.  Fig.  102 


FIG.  102.  —  Repeating  Coil  Suitable  for 
Phantom  Use. 


PHYSICAL.    CKT 


PHANTOM    CKT 


PHYSICAL  CKT 


FIG.  103.  —  Repeating  Coil  Type  of  Phantom  Circuit. 

shows  a  very  efficient  type  of  repeating  coil  as  used  by  the  American 
Telephone  and  Telegraph  Company.     Fig.  103  shows  a  circuit  phan- 


214 


TOLL  TELEPHONE  PRACTICE 


tomed  by  means  of  repeating  coils,  the  operation  of  which  will  be 
clear  from  an  inspection  of  the  drawing. 

Phantom  circuits  are  also  used  as  two-way  order  circuits  between 
toll  operators.  In  this  case  the  passing  of  tickets  and  any  other 
required  exchange  business  can  be  handled  over  this  circuit,  and  con- 
sequently the  physical  circuits  are  always  available  for  regular  service. 
This  is  quite  an  item  to  the  telephone  company,  as  the  subscriber 
only  pays  for  the  time  he  is  actually  talking;  and  if  the  physical  cir- 
cuits are  ordered  up  by  means  of  the  phantom,  they  will  be  revenue- 
producing  a  larger  portion  of  the  time.  A  two-way  phantom  order 
circuit  is  shown  in  Fig.  104,  and  since  the  general  arrangement  of 


TOOPf?.SeT"l 


TO  OPF?SET°2 


FIG.  104.  —  Phantom  Circuit  Used  as  an  Order  Wire. 

the  phantom  is  similar  to  those  already  described,  only  the  special 
features  will  be  explained.  It  will  be  noted  that  the  middle  points 
of  the  repeating  coils  A  and  A'  are  wired  to  the  lever  contacts  of  keys 
K  and  K ',  and  therefore  when  key  K  is  actuated  the  two  following 
circuits  will  be  established.  One  is  completed  from  ground,  by  way 
of  relay  R,  to  the  make  contacts  of  key  K  and  battery.  This  will 
operate  relay  R  and  thus  place  the  operator's  telephone  set  in  circuit 
with  winding  2  of  repeating  coil  A.  The  second  circuit  that  is  com- 
pleted by  the  operation  of  key  K  may  be  traced  from  battery  to  the 
contact  springs  of  key  K  and  thence  by  means  of  the  lever  contacts 
of  said  key  to  the  middle  point  of  winding  i  of  the  repeating  coil  A. 
At  this  junction  the  current  will  divide,  half  of  it  flowing  through  the 


PHANTOM   LINES  215 

upper  portion  of  coil  i  to  the  middle  point  of  coil  i  of  the  repeating 
coil  B,  thence  over  the  line  wires  of  circuit  B  to  the  middle  point 
of  coil  i  of  repeating  coil  Bf,  from  which  point  it  may  be  traced  to 
the  middle  point  of  coil  i  of  repeating  coil  Af.  At  this  terminal  the 
current  unites  with  the  other  portion  which  flowed  through  the  lower 
half  of  winding  i  of  repeating  coil  A  and  follows  a  path  over  telephone 
circuit  C,  similar  to  that  outlined  above  for  circuit  B.  The  flow  of 
current  can  now  be  traced  through  relay  Rf  k>  ground.  Consequently 
relay  Rf  will  be  energized  and  thus  the  operators'  sets  will  be  con- 
nected directly  to  windings  2  of  repeating  coils  A  and  A'\  the  operators 
then  communicate  over  the  phantom.  The  restoration  of  key  K  will 
release  the  relays  and  return  the  circuit  to  normal  conditions.  The 
operation  in  the  opposite  direction  is  similar. 

Before  leaving  the  subject  of  phantom  operation,  it  seems  appro- 
priate to  emphasize  some  of  the  precautions  that  should  be  taken. 
As  previously  stated,  the  lines  must  be  well  balanced  as  regards 
capacity,  inductance,  leakage  and  resistance.  For  this  reason  it  is 
advisable  to  keep  the  carbons  on  phantom  lines  scrupulously  clean, 
since  the  accumulation  of  dust  at  this  place  is  very  likely  to  cause  an 
unbalance  which  will  be  noticeable.  In  order  to  obviate  inductive, 
disturbance  an  extensive  system  of  transposition  must  be  resorted  to; 
in  the  first  place,  the  individual  wires  of  each  physical  circuit  must 
be  regularly  transposed  and,  secondly,  the  two  wires  of  one  physical 
circuit  (which  compose  one  lead  of  the  phantom)  must  be  transposed 
with  the  wires  of  the  other  physical  circuit  (which  constitutes  the 
other  conductor  of  the  phantom).1  If  these  provisions  are  not  care- 
fully observed,  inductive  disturbances  are  almost  certain  to  manifest 
themselves.  However,  when  the  phantom  is  well  balanced,  the 
transmission  is  often  slightly  superior  to  that  obtained  over  the 
physical  circuits. 

1More  will  be  said  of  this  in  Chapter  XIX,  which  treats  of  transposition  systems. 


CHAPTER  XV 
TEST  AND   MORSE  BOARDS 

THE  three  preceding  chapters  describe  the  conventional  circuits  and 
give  the  general  theory  upon  which  the  principles  of  composite,  sim- 
plex and  phantom  work  are  based.  This  is  but  half  the  problem, 
however,  and  it  is  the  purpose  of  this  chapter  to  describe  the  methods 
of  applying  these  principles  to  actual  practice.  The  work  of  com- 
positing or  phantoming  is  seldom  if  ever  resorted  to  at  the  toll  board; 
and  although  in  some  of  the  smaller  offices  the  wire  chief's  desk  is 
provided  with  the  necessary  equipment  for  handling  this  type  of 
service,  the  best  practice  is  to  have  an  entirely  separate  and  distinct 
board  termed  the  test  and  morse  board.  It  should  be  borne  in  mind, 
in  reading  the  following  description,  that  the  desired  end  in  this  work 
is  flexibility,  which  is  naturally  essential  in  all  switchboards,  but 
especially  for  the  board  under  discussion,  due  to  the  great  variety  of 
combinations  that  are  necessary. 

Test  and  morse  boards  may  be  readily  grouped  in  two  general 
classes,  one  in  which  cords  and  plugs  are  employed  in  making  the- 
various  connections  and  the  other,  sometimes  known  as  "  cordless 
boards,"  requiring  the  use  of  plugs  only  to  change  the  normal  lay- 
out, the  jack  contacts  being  used  for  switching  purposes  except  in 
emergencies.  The  first  type  is  the  more  flexible  of  the  two  and  is  con- 
sequently better  adapted  for  small  equipments.  Each  of  these  sys- 
tems is  in  general  use  and  merits  description,  and  since  the  cord  and 
plug  type  was  the  first  to  be  adopted,  it  will  receive  attention  first. 

The  lines  entering  the  ordinary  test  board  are  of  three  classes; 
namely,  toll  lines,  local  trunks  and  long  distance  or  toll  terminals, 
the  latter  embracing  both  telegraph  and  telephone  subscribers'  drops. 
The  toll  lines  present  the  greatest  degree  of  complication  and  will  be 
treated  at  length. 

Fig.  105  shows  the  ordinary  toll-line  circuit,  which,  after  passing 
through  the  standard  protection,  is  looped  through  six  jacks.  This 
wiring  results  in  a  very  flexible  layout,  as  by  means  of  these  jacks  the 

216 


TEST  AND  MORSE  BOARDS 


217 


wire  chief  is  enabled  to  cut  off  the  switchboard  end  of  the  circuit  and 
remain  bridged  on  the  toll  line  and  vice  versa.  The  functions  of  this 
circuit  will  be  readily  appreciated  as  the  description  of  the  board 
progresses.  The  jacks  are  arranged  in  pairs,  being  numbered  in  the 
figure,  i,  2  and  3  respectively.  It  will  be  observed  that  if  a  twin 
plug  be  inserted  in  pair  3,  the  apparatus  connected  to  the  cord  will 
be  bridged  across  the  toll  line  and  the  switchboard  end  of  the  circuit 


TO  SW.BP. 


FIG.  105.  —  Toll-line  Circuit  at  Test  Board. 

will  be  disconnected.  If  the  plug  is  inserted  in  pair  i,  however,  the 
equipment  connected  to  the  cord  will  be  in  connection  with  the  switch- 
board. Plugging  into  pair  2,  in  addition  to  operating  the  busy  sig- 
nal at  the  toll  switchboard  by  means  of  the  make  contact  in  the  jack, 
will  connect  the  cord  equipment  to  the  toll  line.  Therefore  this 
pair  of  jacks  is  ordinarily  used  for  testing,  so  that  the  operators  may 
know  that  the  line  is  in  use.  The  jacks  as  shown  in  the  circuit  are 
mounted  in  vertical  panels  in  the  face  of  the  board  and  are  conse- 
quently very  accessible  to  the  cord  circuits. 

The  first  of  the  cord  circuits  that  will  be  discussed  is  the  regular 
composite  circuit  shown  in  Fig.  106.  The  apparatus  shown  in  the 
diagram  is  the  same  as  that  described  in  Chapter  XIV  and  a  full  de- 
scription is  unnecessary.  It  will  be  noted  that  the  circuit  shows  two 
single  and  two  twin  plugs;  the  single  plugs  are  the  morse  legs  and  the 
twin  plugs  are  respectively  the  line  and  the  drop  sides.  When  it  is 
desired  to  composite  one  of  the  regular  toll  lines,  the  wire  chief  will 
insert  the  twin  plug  marked  "  switchboard  "  in  jacks  i  (Fig.  105) 
and  the  twin  plug  marked  "  line  "  in  jacks  3.  The  two  plugs  marked 
"  morse  leg  "  are  then  inserted  into  the  jacks  which  lead  to  the  morse 


2l8 


TOLL  TELEPHONE  PRACTICE 


board  or  the  morse  subscribers'  equipment.  The  operation  of  the 
circuit  has  already  been  explained  in  Chapter  XIII.  It  will  therefore 
be  evident  that  by  means  of  the  circuit  shown  in  Fig.  106,  any  toll 
line  entering  the  test  board  can  be  composited  with  ease  and  rapidity. 


MORSE  LEG, 


FIG.  106.  —  Composite  Cord  Circuit  at  the  Test  Board. 

In  case  it  is  desired  to  simplex  one  of  the  regular  toll  lines,  the  circuit 
shown  in  Fig.  107  is  utilized.  The  twin  plugs  are  inserted  in  jacks  i 
and  3  of  the  line  circuit  shown  in  Fig.  105  and  the  single  plug  is  in- 
serted in  a  jack  which  is  wired  to  the  morse  equipment. 


FIG.  107.  —  Simplex  Cord  Circuit  at  the  Test  Board. 

'The  battery  for  the  operation  of  these  morse  circuits  is  also  carried 
to  jacks  that  are  located  in  the  test  or  morse  board.  The  method 
of  wiring  is  shown  in  Fig.  108,  from  which  it  will  be  observed  that  the 
battery  leads  are  looped  through  three  jacks.  These  three  jacks  are 
mounted  in  a  row  straight  across  the  battery  panel;  and  the  number 
of  these  jacks  depends  upon  the  size  of  the  office  and  the  extent  of 
the  morse  service.  Naturally,  the  principal  function  of  this  circuit 
is  the  feeding  of  battery,  but  it  is  also  available  for  monitoring  pur- 


TEST  AND  MORSE  BOARDS 


219 


poses.  Thus  it  will  be  observed  that  by  plugging  into  jack  i,  battery 
will  be  fed  out  on  the  two  strands  of  the  cord;  while  if  the  plug  is 
inserted  in  jack  2  the  apparatus  wired  to  the  plug  will  be  cut  in  series 
with  the  regular  circuit.  For  example,  suppose  that  the  regular 
battery  tap  has  been  taken  from  jack  i,  and  that  the  wire  chief  has 
inserted  another  plug,  to  which  is  attached  a  standard  morse  set,  in 
jack  2.  This  will  establish  a  circuit  from  battery  through  jack  3  to 


FUSE: 


FIG.  108.  —  Battery  Jacks  at  the  Test  Board. 

the  tip  and  ring  springs  of  jack  2,  where  by  virtue  of  the  plug  inserted, 
the  battery  will  flow  from  the  ring  spring  of  the  jack  through  the 
morse  apparatus,  and  thence  to  the  tip  spring  of  the  jack,  being 
traced  from  there  to  the  conductor  springs  of  jack  i  and  then  to  the 
morse  circuit.  Consequently  the  current  used  by  this  circuit  must 
all  flow  through  the  monitoring  apparatus  attached  to  jack  2,  and 
the  wire  chief  or  monitor  is  therefore  enabled  to  obtain  a  rapid  and 
accurate  conception  of  the  condition  of  the  circuit.  Jack  3  of  the 
circuit  is  used  for  cutting  off  the  battery  entirely;  this  arrangement  is 
not  universally  used  but  has  been  found  very  convenient. 


SOUNDER 


'.KEY 


FIG.  109.  —  Telegraph  Monitoring  and  Test  Circuit. 

Attention  is  now  called  to  the  circuit  shown  in  Fig.  109,  which 
embodies  the  monitoring  circuit  above  referred  to  as  well  as  the  usual 
morse  testing  circuit.  Plug  2  is  the  monitoring  plug,  the  insertion 


220 


TOLL  TELEPHONE  PRACTICE 


of  which  establishes  conditions  as  described  in  the  preceding  para- 
graph, while  the  single  conductor  plugs  i  and  3  are  used  for  testing 
purposes.  Testing  conditions  are  established  by  inserting  one  of 
these  plugs  in  the  jack  of  the  morse  circuit  to  be  tested  and  the  other 
plug  in  the  battery  jack.  The  telegraph  relay  will  then  be  in  series 
with  the  battery  and  the  line,  and  the  conditions  for  testing  will  be 
established. 

The  method  of  monitoring  the  morse  circuits  having  been  duly 
described,  a  description  of  the  telephone  circuit  is  next  essential. 
This  circuit  cannot  be  used  for  monitoring,  for  the  reason  that  it  is 
not  desirable  to  have  the  wire  chief  cut  in  on  a  telephone  connection; 
the  transmission  on  these  circuits  must  be  kept  up  to  the  highest 
point  of  efficiency  and  the  bridging  of  an  additional  telephone  across 
the  line  would  cut  down  the  transmission.  The  telephone  circuit 
referred  to  is  shown  in  Fig.  no,  and  is  nothing  more  than  an  ordinary 


FIG.  no.  —Wire  Chief's  Telephone  Circuit  at  Test  Board. 

operator's  telephone  set  equipped  with  the  usual  secondary  cut-out. 
This  circuit  is  used  by  the  wire  chief  in  talking  to  trouble-men  out  on 
the  line,  and  also  for  ordering  up  composite  and  phantom  sets  at  other 
offices. 

The  successful  operation  of  the  circuits  entering  a  test  board  de- 
pends to  a  great  extent  upon  the  maintenance  of  almost  perfect  elec- 
trical balance,  and  when  it  is  appreciated  that  this  balance  is  sensitive 
even  to  atmospheric  conditions,  the  importance  of  having  proper  and 
efficient  testing  circuits  is  soon  realized.  Therefore,  since  these  test- 
ing circuits  are  most  essential,  the  more  important  ones  will  be  shown 
in  detail. 

In  Fig.  in  is  shown  the  regular  voltmeter  or  ammeter  circuit  with 
which  every  test  board  should  be  equipped,  the  wiring  of  which, 


TEST  AND  MORSE  BOARDS 


221 


though  extremely  simple,  is  very  flexible.  Thus  by  plugging  into 
jack  2  the  meter  will  be  bridged  across  the  circuit  attached  to  the 
plug,  while  by  the  use  of  jacks  i  and  3,  practically  any  combination 
is  possible.  For  instance,  if  it  is  desired  to  determine  whether  or 
not  a  line  is  grounded,  it  becomes  possible,  by  means  of  two  single- 


FIG.  in.  —  Voltmeter  and  Ammeter  Circuit  at  Morse  Board. 

conductor  cords  and  plugs,  to  readily  set  up  a  circuit  which  would 
immediately  give  the  desired  information.  Thus  if  the  regular  bat- 
tery jack  were  connected  to  jack  3,  and  jack  i  to  the  line  under  test, 
a  full  deflection  of  the  voltmeter  would  be  obtained  in  case  the  line 
were  grounded.  The  presence  of  foreign  potentials  can  be  readily 
ascertained  by  inserting  the  cord  from  jack  3  in  one  of  the  ground 
jacks,  or  by  inserting  one  of  the  ground  plugs  directly  in  the  jack. 
This  circuit,  as  previously  stated,  is  most  essential  and  in  the  hands 
of  an  experienced  wire  chief  can  be  used  for  making  almost  every 
conceivable  sort  of  test. 

Another  test  circuit  which  is  used  very  extensively  is  the  "  bridge 
circuit  "  shown  in  Fig.  112.     The  two  plugs  shown  in  the  diagram  are 


FIG.  112.  —  Bridge  Circuit  at  Test  Board. 

inserted  in  either  end  of  the  circuit  that  is  to  be  measured,  thereby 
supplying  the  fourth  or  unknown  arm  of  the  bridge.  The  circuit  is 
self-explanatory  and  will  be  passed  without  further  comment. 


222  TOLL  TELEPHONE  PRACTICE 

There  is  one  more  test  circuit  which  is  sometimes  used  in  the  opera- 
tion of  a  test  board,  namely,  the  galvanometer  circuit  shown  in  Fig. 
113.  This  circuit  is  so  wired  that  galvanometer  measurements  can 
be  made  on  any  line,  direct.  In  case  the  instrument  is  wired  as 
shown  in  the  figure,  the  operation  of  setting  up  the  circuit  is  extremely 
simple.  All  that  is  necessary  is  to  insert  the  battery  plugs  in  the 


BATT.  LINE 


GALVANOMETER 
0-J 


FIG.  113.  —  Galvanometer  Circuit  at  Test  Board. 

proper  battery  jacks  and  the  line  plugs  into  the  jacks  of  the  line  under 
test.  Under  these  conditions  the  galvanometer,  battery  and  line  will 
be  in  series,  and  consequently  the  apparatus  is  connected  in  the 
desired  relation.  Furthermore,  if  it  is  desired  to  use  the  galvanom- 
eter in  connection  with  other  apparatus  the  method  of  wiring  shown  is 
adaptable  to  almost  any  condition. 

This  completes  the  description  of  the  wiring  of  the  principal  cir- 
cuits that  are  found  at  a  board  of  this  character,  and  it  now  becomes 
necessary  to  show  how  these  circuits  are  installed  and  distributed  in 
the  board  itself.  For  this  purpose  reference  will  be  made  to  Fig.  114, 
which  shows  the  face  equipment  of  a  standard  test  board  in  which 
the  different  circuits  will  be  designated.  The  board  is  called  a  through 
test  board  to  distinguish  it  from  the  so-called  terminal  board.  The 
terminal  station,  as  the  name  implies,  is  the  terminus  of  the  line,  i.e. 
it  is  not  intermediate  between  long-distance  offices.  Hence,  in  the 
terminal  station  we  find  a  large  number  of  leased  lines,  usually  occupy- 
ing one  or  two  panels,  whereas  the  function  of  the  through  station 
consists  mainly  of  interconnecting  two  or  more  long-distance  offices. 


TEST  AND  MORSE   BOARDS 


223 


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o  o 

o  o 


o  o 
o  o 
o  'o 


o  o  o 

000 

o  o  o 

000 

o  o  o 

000 

o  o  o 

o  o  o 

o  o  o 

o  o  o 

000 
000 
000 

o  o  o 
o  o  o 

000 


000 
000 
000 

o  o  o 

000 
000 
000 

o  o  o 

000 
000 

o  o  o 

000 

o  o  o 
o  o  o 
o  o  o 

000 

o  o  o 

000 
000 
000 
000 

o  o  o 


00 
00 

o  o 

00 
00 

o  o 

00 


o  o 

O  O 

o  o 

o  o 


o  o 

o  o 

o  o 

o  o 

o  o 

O  O 

o  o 

o  o 

o  o 

o  o 

o  o 

o  o 


r 


WEST 
o  O  O 
000 
O  O  O 

o  o  o 

O  O  O 
000 
000 
000 
000 

o  o  o 
o  o  o 

000 
000 
000 
000 

o  cro 

000 
000 

o  o  o 
o  o  o 

000 
000 

o  o  o 
o  o  o 
o  o  o 

000 

o  o  o 

000 

o  o  o 
o  o  o 
o  o  o 
oop 

000 

o  o  o 

o  o  o 

o  o  o 

o  o  o 

o  o  o 

o  o  o 

o  o  o 


I 
-5 
s 


e  e  e  c  e 
06000 

W.C.TRVJNKS 


O  O  O       000 
"•MCTEK     VOLTMETEH 


o  o  o 

G.KOUNPS 


OPR.TEL.SET 


o        o 

TEST  SET  * 


TEST  SET*Z       LINE       BA.TT. 


«       o 

TEST  SET  ' 


FIG.  114.  —  Jack  and  Key  Equipment  oi  a  Standard  Test  and  Morse  Board. 


224 


TOLL  TELEPHONE  PRACTICE 


FIG.  115.  —  Legless  Telegraph  Key. 


However,  it  will  be  obvious  from  what  has  just  been  said  that  the 
through  station  shown  can  be  easily  converted  into  the  terminal  type 
by  the  addition  of  panels  for  leased  lines. 

The  apparatus  used  in  the  various  circuits  is  all  properly  desig- 
nated on  the  drawing,  to  facilitate  description.  Attention  should 
first  be  given  to  the  four  panels  labeled  "  toll  lines,"  each  consisting 
of  three  complete  vertical  rows  of  jacks.  These  jacks  correspond  to 

the  ones  shown  in  Fig.  105,  from 
which  it  will  be  noted  that  they 
are  arranged  in  pairs,  the  first 
two  horizontal  rows  of  jacks  in 
each  panel  constituting  one  me- 
tallic line,  the  next  two  another 
line,  etc.  As  will  be  observed, 
these  panels  are  labeled  "north," 
"south,"  "east"  and  "west," 
respectively,  which  indicates  that  the  lines  from  the  north  terminate 
in  the  north  panel,  those  from  the  south  in  the  south  panel,  etc.  On 
either  side  of  these  line  panels  are  the  panels  in  which  are  installed 
the  composite  and  phantom  sets  terminating  in  plugs.  Above  each 
of  the  plugs  is  placed  a  desig- 
nation card,  so  as  to  render  the 
location  of  a  particular  circuit 
an  easy  matter.  The  single- 
conductor  morse  legs  of  these 
composite  circuits  are  located  in 
the  panel  marked  "  morse  legs," 
and  these  plugs,  like  the  line 
and  switchboard  plugs,  are  pro- 
vided with  designation  strips  to 
facilitate  location.  In  the  panel 

marked  "  battery  "  are  placed  the  regular  battery  jacks,  the  wiring 
of  which  is  shown  in  Fig.  108.  The  panel  marked  "  repeater  " 
contains  the  jacks  in  which  the  circuits  of  the  telegraph  repeaters 
terminate.  It  might  also  be  well  to  state  in  passing  that  it  is  feasible 
and  sometimes  the  practice  to  multiple  the  composite  plugs  in  several 
panels,  so  as  to  reduce  the  amount  of  equipment  and  still  have  the 
apparatus  convenient  for  connection  with  any  line. 

The  manner  in  which  the  equipment  is  installed  in  the  face  of  the 


FIG.  116.  —  Leg-type  Telegraph  Key. 


TEST  AND  MORSE  BOARDS 


225 


FIG.  117.  —  Telegraph  Sounder. 


board  being  understood,  it  seems  well  to  call  attention  to  the  sim- 
plicity of  the  operation  which  this  arrangement  affords.  Thus  sup- 
pose it  is  desired  to  composite  a  line.  This  is  accomplished  by 
inserting  the  composite  plugs  on 
either  side  of  the  line  panel  in  the 
proper  line  jacks,  and  the  morse 
legs  into  the  desired  leased  lines,  or 
repeater  jacks,  and  the  operation  is 
completed.  Any  other  circuits  that 
are  customarily  set  up  at  this 
board  can  be  established,  by  reason 
of  the  general  arrangement  of  the 
apparatus,  with  equal  dispatch. 

The  regular  line  jacks  are  only 
one  part  of  the  equipment  necessary 
and  attention  will  now  be  directed  briefly  to  the  testing  and  mis- 
cellaneous circuits.  The  apparatus  for  these  is  all  properly  desig- 
nated on  the  drawing  and  therefore  a  very  brief  reference  to  a  few  of 
them  is  all  that  is  necessary.  Thus,  beneath  the  regular  panel  equip- 
ment, in  the  face  of  the  board,  are  found  the  ground  jacks  often  needed 
in  testing,  and  the  voltmeter  and  ammeter  jacks,  which  are  wired  from 

the  instruments  shown 
above  as  indicated  in  Fig. 
in.  There  may  also  be 
seen  the  office  trunk  jacks 
used  for  intercommunica- 
tion between  this  board 
and  the  toll  board  and  the 
various  desks  in  the  office. 
On  the  key  and  plug  shelf 
are  shown  the  equipment 
for  the  regular  test  circuit 
of  Fig.  109,  the  operator's  telephone  circuit  of  Fig.  no,  the  bridge 
circuit  of  Fig.  112,  and  the  galvanometer  circuit  of  Fig.  113.  The 
location  of  this  equipment  needs  no  special  explanation. 

While  in  the  equipment  just  shown  the  plugs  used  in  connection 
with  the  simplex  and  composite  circuits  are  all  in  the  face  of  the 
board,  it  is  sometimes  the  practice  to  have  all  these  plugs  on  the  shelf. 
The  objections  to  the  last  arrangement  are,  first,  the  resulting  tangle 


FIG.  1 1 8.  —Telegraph  Relay. 


226  TOLL  TELEPHONE  PRACTICE 

of  cords  across  the  face  of  the  board  when  a  number  of  connections 
are  up  and,  second,  the  space  on  the  shelf  utilized  by  this  equipment 
is  needed  for  the  testing  apparatus.  However,  notwithstanding  these 
objections,  experience  has  shown  that  for  small  equipments  this  type 
of  board  gives  excellent  satisfaction  and  is  to  be  recommended  in 
preference  to  any  other  arrangement. 

As  already  stated,  test  and  morse  boards  can  be  divided  into  two 
general  groups:  the  first,  in  which  cords  and  plugs  are  employed  in 
making  the  various  connections,  —  the  description  of  which  has  just 
been  completed,  —  and  the  second,  sometimes  known  as  the  cordless 
board,  to  which  the  remainder  of  this  chapter  will  be  devoted.  The 
cordless  board  eliminates,  to  a  considerable  extent,  the  weakest  part 
of  a  switchboard  equipment,  and  in  that  respect  it  is  beneficial,  as  it 
necessarily  avoids  the  annoying  cord  troubles  and  reduces  the  cost  of 
maintenance.  Furthermore,  the  face  of  the  panel  is  not  obstructed 
by  the  many  intersecting  cords,  and  the  location  of  the  equipment  in 
the  board  is,  therefore,  greatly  facilitated.  The  above  statement  may 
raise  the  question  as  to  why  the  cord  equipment  continues  to  be  in 
demand.  It  will  be  understood  upon  a  more  thorough  investigation, 
however,  that  each  type  of  equipment  meets  particular  conditions. 
For  small  equipments,  in  which  the  amount  of  apparatus  necessary 
for  composite,  simplex  and  phantom  work  is  limited,  a  cord  equipment 
is  preferable.  This  follows  directly  from  the  fact  that  cords  permit 
greater  flexibility  than  the  other  type,  which  is  very  essential  in  small 
offices.  For  a  large  equipment,  however,  it  has  been  proved  good 
practice  to  wire  a  composite  set  permanently  in  each  of  the  toll  lines 
entering  the  office.  In  this  case  the  cordless  equipment  is  a  distinct 
advantage  because  the  cord  complication  is  entirely  eliminated  in 
normal  operation. 

Fig.  119  shows  a  standard  toll  line  wired  through  the  test  board. 
As  shown,  the  line  upon  entering  the  office  is  first  wired  through  the 
regular  protection  at  the  main  frame.  From  the  frame  the  tip  side 
of  the  line  can  be  traced  through  the  cut-off  jacks  i  and  3  to  terminal  e 
on  the  composite  distributing  frame,  while  the  ring  side  of  the  line 
is  wired  through  cut-off  jacks  6  and  8  to  terminal/  on  this  frame.  At 
the  frame  the  line  can  be  cross-connected  for  a  direct  telephone  circuit 
without  morse  service,  or  it  may  be  associated  with  a  standard  com- 
posite set. 

Since  the  former  of  these  two  involves  the  simpler  construction  it 


TEST  AND   MORSE   BOARDS 


227 


. 


228  TOLL  TELEPHONE  PRACTICE 

will  be  considered  first.  In  this  case  the  tip  side  of  the  line  is  cross- 
connected  from  terminal  e  to  terminal  d,  as  shown  by  the  dotted 
jumper  wire;  the  line  can  then  be  followed  through  cut-off  jack  4 
to  terminal  j  on  the  intermediate  frame,  while  the  ring  side  of  the  line 
is  cross-connected  from  terminal/  to  c  and  is  wired  from  there  through 
cut-off  jack  9  to  terminal  k  on  the  intermediate  frame.  It  will  be 
noted  that  a  third  terminal  /  is  associated  with  the  line  on  the  inter- 
mediate frame  and  that  this  terminal  is  wired  direct  to  a  make-contact 
on  jack  i  at  the  test  panel.  The  reason  for  this  wiring  will  become 
apparent  in  what  follows.  The  three  terminals  /,  j  and  k  are  cross- 
connected  at  the  intermediate  frame  to  terminals  i,  m  and  n,  respec- 
tively. The  latter  terminals  are  those  wired  to  the  position  of  the  toll 
switchboard  at  which  this  line  is  to  terminate. 

The  above  description  illustrates  the  method  of  wiring  for  a  straight 
telephone  circuit  and  it  is  next  essential  to  show  how  the  line  may  be 
composited.  For  this  purpose  one  must  return  to  the  line  terminals 
e  and /at  the  composite  distributing  frame,  to  which  points  the  circuit 
can  be  traced  in  the  outline  above.  When  it  is  desired  to  composite 
the  line,  the  jumper  wires  ed  and/c  are  removed  and  a  new  set  of  four 
jumpers  replaces  them.  Thus  terminal  e  is  cross-connected  to  ter- 
minal a,  from  which  point  the  tip  side  of  the  line  can  be  traced  through 
cut-off  jack  2  and  then  to  terminal  o  on  the  composite  distributing 
frame,  while  terminal  /  on  this  frame  is  cross-connected  to  b  and  can 
be  traced  from  there  through  cut-off  jack  7  to  terminal  r  on  the  com- 
posite frame.  The  tip  side  of  this  line  is  then  cross-connected  to 
terminal  q,  from  which  point  the  telephone  circuit  can  be  traced 
through  condensers  B  and  D  to  terminal  u  on  the  composite  frame 
and  thence  to  terminal  #,  through  the  line  side  of  the  composite  ringer 
and  terminal  x'  on  the  switchboard  side  of  the  ringer;  from  there  it  can 
be  followed  to  cut-off  jack  5  and  terminal  h  on  the  composite  frame, 
then  by  means  of  jumper  kd  to  cut-off  jack  4  and  thence  to  the 
tip  side  of  the  intermediate  distributing  frame.  The  ring  side  of  the 
line  follows  a  similar  path,  which  can  be  traced  from  terminal  r  on 
the  composite  frame  by  means  of  the  jumper  to  terminal  p\  through 
condensers  N  and  E  to  terminal  z>;  then  by  means  of  jumper  vy 
it  can  be  followed  to  the  line  side  of  the  composite  ringer  and  thence 
from  y'  on  the  switchboard  side  of  the  ringer,  by  means  of  jumper 
y'T,  to  cut-off  jack  10  and  terminal  g  on  the  composite  frame.  The 
lead  is  then  cross-connected  to  terminal  c  and  can  be  traced  by  means 


TEST  AND  MORSE  BOARDS  229 

of  cut-off  jack  9  to  the  ring  side  of  the  intermediate  frame.  When 
the  composite  ringer  is  wired  in  the  circuit,  the  solid-line  jumpers  us 
and  vt  are  omitted.  However,  when  the  line  is  normally  looped 
through  the  office  for  through  service,  the  solid  jumpers  just  referred 
to  are  used,  and  the  dotted  jumpers  to  the  composite  ringers  are 
omitted. 

Having  traced  the  regular  telephone  wiring  for  composite  operation, 
it  remains  to  follow  the  path  of  the  telegraph  circuit.  The  telegraph 
jacks  are  cabled  from  the  morse  panel  to  terminals  on  the  composite 
frame,  as  shown  in  Fig.  119.  The  morse  taps  shown  in  the  circuit 
terminate  at  o'  and  r'  on  the  composite  frame.  The  telegraph  circuit 
on  the  tip  side  of  the  line  can  be  traced  as  follows:  from  terminal  o', 
by  means  of  jumper  o'q',  through  impedance  coil  A,  to  terminal  q  and 
thence  by  means  of  jumper  qo  to  cut-off  jack  2;  from  here  it  can  be 
traced  to  terminal  a  on  the  composite  frame  and  then  by  means  of 
jumper  ae  to  cut-off  jacks  3  and  i  to  .the  line.  The  ring  side  of  the 
line  is  traceable  from  terminal  r',  by  means  of  jumper  r'p',  through 
impedance  coilZ,  to  terminal  p,  and  then  by  way  of  jumper  pr  to  cut-off 
jack  7.  From  here  the  circuit  can  be  followed  to  terminal  b,  through 
jumper  bf,  and  cut-off  jacks  8  and  6  to  the  ring  side  of  the  line. 

It  naturally  follows  that  by  cross-connecting  composite  frame  ter- 
minals a,  b,  c  and  d  to  terminals  e,  /,  g  and  h  respectively,  the  toll  line 
will  be  equipped  for  composite  service;  and  it  also  follows  that  if 
jumpers  fc  and  ed  are  included,  while  the  others  are  omitted,  the  line 
is  free  from  the  composite  apparatus  and  can  be  used  for  straight 
telephone  service  only.  In  some  equipments  the  terminals  a,  b,  c,  d, 
e,  /,  g  and  h  are  located  on  a  connecting  rack  in  the  rear  of  the  test 
panel  instead  of  on  a  separate  frame.  In  the  latter  case  they  may 
form  an  entirely  separate  frame  or  be  located  on  a  part  of  the  inter- 
mediate frame.  Of  these  two  methods  the  one  using  the  separate 
frame  is  the  better,  since  large  connecting  racks,  containing  many 
clips,  should  be  avoided  as  much  as  possible  in  switchboard  designs 
because  they  increase  the  probability  of  office  trouble.  The  connect- 
ing rack  is  inferior,  in  general,  to  the  standard  frame. 

The  purposes  of  the  different  cut-off  jacks  in  Fig.  119  will  now 
be  considered.  These  jacks  are  installed  to  afford,  first,  a  ready 
means  of  testing.  Thus  when  plugs  are  inserted  in  jacks  i  and  6,  the 
line  may  be  tested  out  through  the  main  distributing  frame,  the 
switchboard  portion  of  the  line  being  cut  off.  In  addition  to  this, 


230  TOLL  TELEPHONE  PRACTICE 

the  act  of  inserting  the  plug  in  jack  i  will  close  the  make  contact, 
which  will  ground  the  lead  wired  to  the  terminal  /  of  the  intermediate 
distributing  frame  and  actuate  all  the  busy  signals  associated  with 
this  line.  If  the  plugs  are  inserted  in  jacks  3  and  8  the  line  can  also 
be  tested  out  through  the  main  frame,  but  in  this  case  no  busy  signal 
is  displayed  at  the  board.  The  composite  set  can  be  cut  out  by 
inserting  twin  plugs  horizontally  so  as  to  connect  the  springs  of  jacks 
3  and  4,  and  8  and  9.  By  inserting  a  twin  plug  vertically  in  jacks  2 
and  7,  the  toll  line  is  opened  and  a  test  may  be  made  through  the 
composite  apparatus  to  the  toll  switchboard.  By  inserting  plugs  in 
jacks  4  and  9,  a  test  can  be  made  direct  to  the  switchboard.  A  twin 
plug  inserted  in  jacks  3  and  8  will  cross  the  line  wires,  i.e.,  the  line 
will  enter  the  office  by  means  of  jacks  i  and  3  and  will  be  carried  out 
direct  by  means  of  the  twin  plug  and  jacks  8  and  6.  The  use  of  the 
battery  and  loop  jacks  in  the  morse  panel  will  be  explained  in  what 
follows,  in  connection  with  the.  face  equipment. 

The  description  of  the  standard  circuit  used  for  composite  operation 
in  connection  with  a  cordless  equipment  being  now  completed,  it  be- 
comes essential  to  show  the  circuit  used  for  simplex  and  phantom  work; 
and  in  this  connection  reference  will  be  made  to  Fig.  1 20.  It  must  be 
borne  in  mind  that  in  simplex  work  the  two  line  leads  of  the  telephone 
circuit  are  operated  in  parallel  for  morse  purposes,  in  place  of  using 
each  lead  of  the  telephone  line  for  a  telegraph  circuit  as  in  composite 
work.  For  phantom  operation,  furthermore,  two  telephone  circuits 
are  required,  the  two  leads  of  each  individual  circuit  being  operated 
in  parallel  as  one  of  the  telephone  leads  for  the  phantom  circuit. 
Fig.  1 20  shows  two  toll  lines  entering  an  office,  each  of  which  may  be 
used  for  a  simplex  circuit ;  or  by  using  the  two  in  conjunction  a  phan- 
tom telephone  circuit  may  be  derived. 

Since  the  wiring  of  line  i  is  identical  with  line  2  in  the  composite 
panel,  a  description  of  line  i  will  suffice.  The  tip  side  of  the  line, 
after  passing  through  the  protection  at  the  main  frame,  is  looped 
through  cut-off  jacks  i,  3  and  2  respectively;  and  from  there  is  wired 
through  winding  i  of  coil  A,  through  jacks  7,  8  and  6  and  thence  back 
to  the  ring  side  of  the  line.  From  the  middle  point  of  winding  i  of 
coil  A,  the  morse  tap  is  wired  to  jack  n  in  the  morse  panel.  The 
tip  side  of  the  switchboard  end  of  this  circuit  is  looped  through  cut-off 
jacks  4  and  5,  and  is  then  wired  through  winding  2  of  coil  A  to  jacks 
10  and  9  respectively,  and  back  to  the  ring  side  of  the  switchboard 


TEST  AND   MORSE   BOARDS 


231 


end  of  the  line.  Therefore  when  it  is  desired  to  simplex  the  above 
circuit,  a  plug  is  inserted  in  jack  n.  This  plug  is  attached  to  a  cord, 
which  is  equipped  with  a  similar  plug  at  the  other  end,  and  the  latter 


PHANTOM  SERIES 


FIG.  120.  —  Simplex  and  Phantom  Connection  at  a  Cordless  Test  Board. 

is  inserted  in  a  jack  which  leads  either  to  the  proper  telegraph  appara- 
tus or  the  morse  subscriber. 

If  a  phantom  circuit  is  to  be  established,  however,  the  plug  inserted 
in  the  morse  jack,  referred  to  above,  is  plugged  in  jack  2  of  the 
series  of  phantom  jacks,  and  a  similar  connection  is  made  between 


232  TOLL  TELEPHONE  PRACTICE 

» 

jack  15  of  the  morse  panel  and  jack  7  of  the  phantom- jack  series. 
This  connection  is  shown  in  the  figure  by  means  of  broken  lines.  The 
tip  side  of  the  phantom  circuit  may  then  be  traced  from  the  toll 
switchboard  through  jacks  4,  3,  i  and  2  respectively,  of  the  phantom- 
jack  series,  to  jack  n  of  the  morse  panel  and  thence  to  the  middle 
point  of  winding  i  of  coil  A ;  from  here  it  can  be  traced  through  jacks 
2,  3  and  i,  and  7,  8  and  6  out  onto  the  two  wires  of  toll  line  i.  The 
ring  side  of  the  phantom  circuit  can  be  similarly  traced  to  and  through 
the  phantom-jack  series  to  jack  15  of  the  morse  panel,  thence  to  the 
middle  point  of  winding  i  of  coil  A  of  line  2  and  then  out  onto  the  line. 
From  what  has  preceded,  it  can  be  readily  seen  that  the  matter  of  sim- 
plexing  or  phantoming  at  the  morse  panel  is  a  simple  operation. 

The  function  of  the  different  cut-off  jacks  on  the  toll  line,  as  well 
as  in  the  phantom  series,  is  for  the  purpose  of  testing,  as  in  the  com- 
posite circuit  previously  explained.  Thus  by  plugging  into  jacks  i 
and  6  a  test  may  be  made  out  on  the  line,  the  necessary  busy  test  being 
displayed  at  the  toll  board  while  the  switchboard  equipment  is  cut 
off  from  the  circuit.  By  plugging  into  jacks  3  and  8  the  line  is  free 
from  the  switchboard  equipment,  but  in  this  case  no  busy  signal  is 
displayed  at  the  board;  while  plugging  into  jacks  2  and  7  cuts  off  the 
line  and  a  test  can  be  obtained  through  coil  A  to  the  switchboard. 
Plugging  into  jacks  4  and  9  makes  possible  a  direct  test  to  the  switch- 
board. In  fact  the  jacks  in  this  circuit  serve  the  identical  purpose  of 
those  shown  and  described  for  the  composite  circuit. 

The  manner  in  which  the  jacks  are  mounted  in  the  board  is  inter- 
esting; Fig.  121  shows  a  section  of  the  test  panel.  As  shown  in 
the  diagram,  the  first  panel  of  jacks  takes  the  toll  lines,  each  line 
requiring  five  pairs  of  jacks  straight  across  the  panel.  These  jacks 
are  wired  as  per  the  jack  series  numbered  i  to  10,  shown  in  the  com- 
posite circuit  in  Fig.  119  and  in  the  simplex  and  phantom  circuit  in 
Fig.  1 20.  The  two  upper  rows  of  jacks  on  the  face  equipment  draw- 
ing'have  been  numbered  to  facilitate  the  explanation.  To  distin- 
guish whether  a  certain  set  of  jacks  is  wired  for  composite,  simplex  or 
phantom  work,  the  panel  is  equipped  with  designation  cards  directly 
to  the  right  of  each  set  of  jacks.  It  might  be  well  to  add  here  that  the 
two  extra  jacks  in  the  phantom  series  of  the  circuit  in  Fig.  120,  which 
are  not  wired,  are  simply  placed  in  the  toll-line  panel  to  make  it  uni- 
form. In  the  next  panel  is  located  the  jack  series  numbered  n  to  18 
in  the  above-mentioned  circuits.  This  panel  is  termed  the  morse 


TEST  AND  MORSE  BOARDS 


233 


panel,  since  all  telegraph  and  phantom  connections  are  put  up  by 
means  of  these  jacks.  In  the  next  panel  to  the  right  are  located  the 
morse  subscribers'  jacks,  to  which  are  wired  the  leased  lines  as  shown 


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FIG.  121.  —  Face  Equipment  of  a  Cordless  Test  and  Morse  Board. 

in  Fig.  122.  These  jacks  are  either  wired  direct  to  the  telegraph 
apparatus  at  the  morse  subscriber's  station  or  to  four-point  switches 
as  shown  in  the  sketch. 

The  advantage  of  the  arrangement  shown  consists  in  providing  a 
means  by  which  the  morse  subscriber  can  readily  "call  the  toll  office 
when  not  plugged  up  for  telegraph  service.  Thus  suppose  a  sub- 
scriber desires  telegraph  service  on  some  special  occasion  outside  of 
.the  regular  scheduled  hours.  If  his  line  were  wired  direct  to  the 
telegraph  instrument,  he  would  have  no  direct  means  of  calling,  and 


234  TOLL  TELEPHONE  PRACTICE 

would  consequently  have  to  call  up  from  a  local  telephone.  With 
the  circuit  as  shown  in  Fig.  122,  however,  it  is  merely  necessary  to 
throw  the  switch  to  the  telephone  apparatus,  when  the  toll  operator 
can  be  called ;  the  latter  will  switch  the  morse  subscriber  to  the  wire 
chief,  who  will  then  attend  to  his  needs.  Then  when  the  plug  for 


TOTEU. 


TOLL   SWBP. 

FIG.  122.  —  Leased  Line  Circuit. 

morse  service  is  inserted  in  jack  i ,  the  toll  switchboard  will  be  cut  off 
by  means  of  the  break  contacts  in  the  jack,  and  the  telegraph  appara- 
tus at  the  subscriber's  premises  can  be  placed  in  circuit  by  throwing 
the  switch  to  normal. 

The  method  of  handling  the  telephone  layout  for  simplex,  composite 
and  phantom  operation  has  been  fully  discussed,  but  very  little  has 
been  said  regarding  the  operation  of  the  battery  panel.  By  referring 
to  Fig.  119,  it  will  be  noted  that  a  short-circuited  twin  plug  inserted 
in  jacks  19  and  20  and  one  inserted  in  jacks  23  and  24  will  place  nega- 
tive and  positive  battery  on  the  springs  of  jacks  14  and  18  respectively. 
Therefore,  if  a  plug  with  a  morse  set  attached  is  inserted  in  either  of 
the  jacks  numbered  12,  13,  14,  16,  17  or  18,  supervision  or  service  can 
be  directly  obtained.  The  loop  jacks  are  wired  in  each  side  of  the 
line  for  flexibility  and  convenience.  Jacks  n  and  15  in  the  morse 
panel  are  used  for  putting  up  leased  lines  or  phantom  connections; 
and  they  are  therefore  so  wired  that  by  plugging  into  them  the  re- 
mainder of  the  morse  circuit  is  cut  off  by  the  break  contacts.  In 
case  it  is  desired  to  place  a  telegraph  repeater  in  the  circuit,  it  can  be 
plugged  into  jack  1 1  or  1 5  of  the  incoming  line  while  the  opposite  tap 
is  plugged  into  jack  n  or  15  of  the  outgoing  line. 

The  general  construction  of  a  test  board  is  identical  with  that  em- 
ployed for  local  boards.  The  framework  of  the  section,  which  bears 
the  weight  of  the  apparatus  and  the  mechanical  strains,  is  made  of 
angle  iron.  This  frame  is  reinforced  and  covered  by  a  wooden  cabinet 
of  proper  design  to  give  it  a  pleasing  appearance. 

The  face  of  the  board  on  which  the  various  jacks  are  mounted  is 


TEST    AND  MORSE  BOARDS 


235 


(Q; 

© 
© 
© 
© 

— — • 

© 

© 

© 

© 
© 


© 
© 

"*» — 

© 
© 
© 

© 


SCC.  A-B 


SPRINQ  JACKS 


SPRING  JACK 


RUBBER 


FIG.  123.  —  Construction  of  Jack  Panels  for  Test  and  Morse  Boards. 


236  TOLL  TELEPHONE  PRACTICE 

built  of  either  solid  hard  rubber  panels,  or  it  may  be  made  of  sheet 
brass  on  either  face  of  which  is  mounted  a  sheet  of  hard  rubber.  The 
former  construction  is  used  mostly  for  small  equipments,  while  the 
latter  is  used  for  large  equipments  almost  exclusively.  The  panel 
construction  for  large  boards  is  shown  in  Fig.  123,  from  which  it  will 
be  noted  that  the  body  of  the  panel  is  made  of  solid  brass,  which  car- 
ries the  mechanical  strain  of  the  equipment,  the  rubber  sheet  being 
used  for  insulation  purposes  only.  In  addition  to  the  hard  rubber 
which  is  fastened  to  each  side  of  the  brass  strip,  e^,ch  jack  hole  is 
equipped  with  a  rubber  bushing  to  insulate  the  sleeve  of  the  line  jacks 
from  the  brass  strip.  The  panel  construction  shown  in  Fig.  123  has 
been  found  practical,  since  brass  is  not  affected  materially  by  heat, 
and  consequently  the  jacks  mounted  on  a  panel  of  this  type  are  not 
thrown  out  of  alignment  due  to  the  ordinary  temperature  variations. 
This  is  of  vital  importance,  since  a  very  slight  contraction  or  expansion 
of  the  material  upon  which  the  jacks  are  mounted  would  make  the 
use  of  twin  plugs  practically  impossible.  The  brass  sheet  also  acts 
as  a  reinforcement  for  the  hard  rubber,  in  that  it  keeps  the  rubber 
panel  from  either  warping  or  buckling,  since  the  same  is  rigidly  at- 
tached to  the  sheet  brass.  This  type  of  panel  construction  has  met 
with  great  success  in  practice. 


CHAPTER  XVI 
SMALL  TEST  PANELS 

THE  test  and  morse  boards  described  in  the  last  chapter  are  designed 
for  offices  of  considerable  size  and  are  rather  elaborate  and  expensive 
for  the  smaller  toll  systems.  An  efficient  type  of  test  board  is  just 
as  essential  in  the  small  systems,  however,  as  in  those  previously 
described.  This  fact  has  received  somewhat  tardy  recognition,  but 
such  equipments  have  recently  been  standardized  and  merit  special 
attention  because  of  their  extensive  field  of  use.  The  smaller  com- 
panies are  commencing  to  realize  that  a  test  board,  or  panel,  is  of 
great  benefit  in  handling  toll  lines,  particularly  in  relation  to  phantom 
circuits  and  derived  telegraph  circuits. 

Small  toll  stations  very  seldom  have  any  use  for  simplex  or  com- 
posite equipment,  since  the  demand  for  leased  telegraph  circuits  is 
generally  restricted  to  large  business  centers.  While  this  is  a  fact 
it  is  nevertheless  true  that  the  telegraph  can  often  be  used  economically 
for  ordering  up  telephone  connections  on  busy  toll  circuits.  This 
reserves  the  circuits  for  revenue  production  exclusively,  since  their 
use  by  the  operator  in  establishing  connections  is  thus  eliminated. 

There  are  several  ways  in  which  the  apparatus  required  for  phantom 
operation  may  be  installed.  In  some  cases,  the  coils  used  to  create 
a  phantom  circuit  are  permanently  wired  in  the  circuit.  This  prac- 
tice would  seem  satisfactory  if  the  lines  are  to  be  continually  oper- 
ated on  a  phantom  basis.  But  as  this  is  frequently  not  the  case,  it 
is  better  practice  to  insert  the  coils  in  the  circuits  in  such  a  manner 
that  they  can  be  readily  removed,  making  it  possible  to  obtain  a  clear 
circuit  for  testing  purposes,  which  is  always  essential. 

In  order  that  the  equipment  shall  possess  this  desired  flexibility, 
means  must  be  provided  for  switching  the  various  coils  in  and  out  of 
the  line  with  the  least  amount  of  trouble,  the  continuity  of  the  line 
being  maintained,  while  this  is  accomplished.  The  amount  of  appa- 
ratus that  is  cut  into  the  circuit  for  this  purpose  should  be  reduced 
to  a  minimum,  so  as  to  prevent  the  increase  of  office  troubles.  How- 

237 


238 


TOLL  TELEPHONE  PRACTICE 


ever,  the  possibility  of  additional  trouble  with  apparatus  which  has 
been  properly  designed  and  correctly  installed  is  very  small. 

The  types  of  test  panels  used  for  this  purpose  should  therefore 
be  substantially  built,  of  simple  design  and,  above  all,  of  moderate 


FIG.  124.  —  Forty- wire  Test  Panel. 

cost.  Two  views  of  a  test  panel  which  possesses  these  essential 
characteristics  are  shown  in  Fig.  124.  This  panel  is  typical  of  the 
Kellogg  Switchboard  and  Supply  Company's  manufacture.  It  is 
designed  for  an  ultimate  capacity  of  forty  wires,  or  twenty  metallic 
circuits,  and  six  pairs  of  phantom  connecting  cords;  the  equipment 


SMALL  TEST  PANELS 


239 


shown  in  the  figure  consists  of  jacks  for  seven  metallic  lines  and  four 
cord  circuits.  The  provision  of  space  for  additional  equipment  is 
generally  advisable,  since  the  increased  cost  of  the  larger  cabinet  is 
merely  nominal  and  the  future  growth  of  the  equipment  can  rarely 
be  predetermined  with  great  accuracy.  The  view  to  the  left,  in' 
Fig.  124,  shows  the  panel  with  the  cover  removed  and  displays  the 
ease  with  which  soldered  connections  on  the  jacks  may  be  examined, 
as  well  as  the  simplicity  with  which  additional  equipment  may  be 
installed. 

Fig.  125  shows  a  panel  of  different  design,  which  is,  arranged  for 
an  ultimate  of  twenty  wires  or  ten  metallic  circuits.     Panels  of  this 


FIG.  125.  —  Twenty-wire  Test  Panel. 

type  can  be  made  for  any  desired  number  of  lines,  but  it  is  found 
convenient  to  divide  the  equipment  into  two  or  more  panels  when 
more  than  forty  wires  are  to  be  accommodated.  This  is  due  to  the 


240  TOLL  TELEPHONE  PRACTICE 

fact  that  it  is  hardly  good  practice  to  mount  more  than  two  rows  of 
jacks  on  the  same  panel,  because  of  the  difficulty  which  would  be 
encountered  in  inspecting  the  jack  contacts.  In  case  several  rows  of 
jacks  are  desired,  this  difficulty  could  be  avoided  by  hinging  the  panel 
so  that  it  might  be  swung  away  from  the  back  board,  thus  making 
the  jacks  accessible.  This  type  of  construction  can  hardly  be  recom- 
mended, however,  since  it  complicates  the  wiring  in  the  respect  that 
provisions  have  to  be  made  for  the  necessary  movement  of  the  panel. 
Two  or  more  panels  similar  to  those  shown  are  sometimes  mounted 
on  one  back  board,  each  panel  having  a  separate  cover  or  case;  this 
is  by  far  the  better  construction,  when  a  larger  capacity  becomes 
necessary. 

The  two  types  of  toll  test  panels  just  shown  are  provided  only  with 
line  jacks,  and  phantom,  composite  and  simplex  cord  equipment. 
However,  these  panels  are  often  equipped  with  a  tele- 
phone set  and  associated  cords,  to  provide  for  talking 
and  ringing  on  the  lines  at  the  panel.  A  panel  of  the 
Western  Electric  Co.'s  type  having  a  capacity  of  twenty- 
one  wires  is  illustrated  in  Fig.  126. 

The  jack  panels  or  mounting  strips  used  for  these 
smaller  equipments  should  be  of  the  same  rigid  design 
as  that  described  for  the  large  boards  in  Chapter  XV. 
As  must  be  evident  from  the  illustrations,  this  type  of 
panel  is  designed  to  mount  on  the  wall  or  some  other 
convenient  support;  hence  the  coils  required  for  phan- 
tom operation  are  not  mounted  in  the  cabinet,  but 
placed  at  some  convenient  location  near  by  and  con- 
nected to  the  panel  by  means  of  a  suitable  cable.  This 
practice  of  locating  the  coils  outside  of  the  cabinet 

FIG.  126.--  prreatly  reduces  the  weight  and  the  strain  on  the  sup- 
Western   Elec-  t          J . 
trie  Company's  ports;  it  also  permits  of  the  use  of  a  much  smaller  and 

.Twenty-one  less  expensive  cabinet. 

Wire  Toll  Test  The  usual  metnod  of  wiring  panels  of  this  type  is 
shown  in  Fig.  127,  which  requires  four  jacks  for  each 
metallic  line.  As  shown  in  the  circuit,  the  line  wires  after  passing 
through  the  standard  protection  of  fuse  and  lightning  arresters  are 
connected  to  the  single-conductor  jacks  on  one  side  of  the  test  panel. 
From  this  point  the  circuit  can  be  traced  through  the  single-conductor 
jack  contacts  to  the  jacks  on  the  other  side  of  the  panel,  from  which 


SMALL  TEST  PANELS 


241 


they  are  wired  direct  to  the  switchboard.  The  panels  are  often 
equipped  with  two  double-conductor  jacks  instead  of  four  single-con- 
ductor jacks  per  line,  for  the  purpose  of  reducing  the  jack  panel 
space  and  the  initial  cost  of  the  equipment.  However,  this  practice 


3W  BD 
JACKS 


LINE 
JACKS 


TO 
SW  BD. 


TO 
LINE 


SYVBD 


FIG.  127.  —  Wiring  of  Line  Circuit  for  Small  Test  Panel. 

sacrifices  part  of  the  flexibility  and  in  a  measure  increases  the  possi- 
bility of  poor  contacts  at  the  jacks,  since  a  single-spring  contact  is 
depended  upon  in  place  of  the  double-spring.  For  these  reasons, 
the  use  of  two  double-conductor  jacks  per  circuit  seems  to  be  false 
economy. 

The  common  method  of  arranging  the  jacks  in  the  panel  is  shown 
in  Fig.  128.  The  line  jacks  are  grouped  on  one  side  of  the  panel  and 
the  switchboard  jacks  on  the  other.  There  are 
two  general  methods  of  designating  the  different 
jacks,  so  that  they  may  be  readily  associated  with 
the  circuits  to  which  they  belong.  One  method  is 
to  stamp  the  number  of  the  jack  in  the  rubber 
panel,  as  shown  in  Fig.  128,  while  in  the  other 
method  small  card  holders  or  designation  strips  are 
mounted  at  the  right  of  the  line  jacks  and  the  left 
of  the  switchboard  jacks,  as  indicated  in  Fig.  126. 
The  latter  method  is  undoubtedly  the  better  prac- 
tice, since  the  cards  used  in  connection  with  the 
designation  strip  may  contain,  in  addition  to  the 
number  of  the  circuit,  the  destination. 

The  directions  which  follow  regarding  the  method 
of  cabling  and  the  size  of  the  wire  best  suited 
for  these  small  equipments  seem  appropriate,  be- 
cause this  part  of  the  installation  is  very  frequently  executed 
in  a  haphazard  and  unworkmanlike  manner,  which  is  conducive  to 
much  trouble.  It  is  best  to  run  a  factory-made  cable  direct  from 
the  line  jacks  at  the  toll  board  to  the  switchboard  jacks  at  the  test 
panel,  and  from  the  corresponding  jacks  on  the  line  side  of  the  panel 


FIG.  128.  —  Jack 
Arrangement  in 
Small  Test  Panel. 


242  TOLL  TELEPHONE  PRACTICE 

another  factory-made  cable  should  be  used  to  carry  the  lines  to  the 
arresters.  All  the  cable  used  in  this  connection  should  be  composed 
of  No.  i4ori6B.  &S.  twisted  pair  wires,  each  wire  having  an  insula- 
tion of  two  wrappings  of  silk  and  one  of  cotton.  The  wires  marked 
A  and  B  in  Fig.  127  are  usually  No.  18  B.  &  S.  bare,  tinned,  copper 
wire  straps,  this  kind  of  wire  being  used  for  all  the  local  wiring  in 
the  jacks. 

For  larger  offices,  it  is  often  convenient  to  be  able  to  cross-connect 
the  lines  so  as  to  distribute  the  load  between  the  various  operators. 
The  wiring  which  should  then  be  used  is  shown  in  Fig.  129.  The 


SW.    BO.  1.1  NE 

JACKS  JACKS 


TO 
SWITCHBOARD  I  A  c  J  I— .  LINE 


CROSS 


.  _____ 

<»  "P*  ra  CONNECTING  H  **t  X~" 

P  I    *[j        RACK  fcU   *  -f  \ 


FIG.  129.  —  Line  Wiring  of  Small  Test  Panel,  Arranged  for  Cross-Connection. 

leads  A  and  B  from  the  back  contacts  of  the  jacks  on  the  switchboard 
side  of  the  panel,  and  C  and  D  from  the  line  jacks,  are  wired  to  a 
cross-connecting  rack,  where  they  may  be  interconnected  as  desired. 
A  convenient  and  simple  arrangement  for  such  an  equipment  is  shown 
in  Fig.  130,  which  is  sufficiently  clear  to  make  a  further  description 
unnecessary. 

This  panel  is  typical  of  the  class  commonly  known  as  toll  test  board 
extensions,  in  which  no  plug  shelf  or  cord  equipment  is  provided,  and 
in  which  the  coils  used  in  the  phantom  and  simplex  connections  ter- 
minate at  the  panel  in  jacks,  in  place  of  cords.  A  forty-one  wire 
extension,  as  manufactured  by  the  Western  Electric  Company,  is 
illustrated  in  Fig.  131;  no  provision  is  made  for  cross-connection. 
The  method  of  connecting  the  coils  into  the  circuit  with  this  class  of 
equipment  is  indicated  in  Fig.  132;  the  line  jacks  being  connected  by 
patching  cords  to  the  jacks^that  are  wired  to  the  coils.  The  figure 
shows  a  line  circuit  connected  as  one  side  of  a  phantom,  according 
to  the  retardation  coil  method;  the  middle  point  of  the  coil  is  con- 
nected to  a  phantom  jack  at  the  panel.  Then,  if  two  physical  lines 
are  thus  connected,  and  the  two  phantom  jacks  are  connected  by 
means  of  patching  cords  to  two  switchboard  jacks,  the  phantom 
line  thus  obtained  will  appear  at  the  toll  switchboard  like  any  other 


CABLE 


=»IO 
SW.  W.  TERMINAL 


5— 


10= 

LINE  TERMINAL 


* 


FIG.  130.  —  General  Arrangement  of  Apparatus  for  a  Small  Test  Panel. 


(243) 


244 


TOLL  TELEPHONE  PRACTICE 


toll  line.  This  method  of  putting  up  phantom  connections  is  not  as 
convenient  or  rapid  as  the  one  in  which  cord  circuits  are  used.  These 
test  board  extensions  are  used  especially  for  toll- 
line  testing  and  patching,  as  described  in  Chapter 
XXI,  on  line  maintenance. 

In  this  connection  it  seems  well  to  emphasize 
the  fact  that  all  toll  stations,  no  matter  how  small, 
should  be  provided  with  some  means  for  making 
simple  line  tests.  This  does  not  imply  that  every 
station  should  be  provided  with  expensive  test- 
ing instruments,  but  the  simple  preliminary  tests 
should  be  possible  at  any  station  where  line  trouble 
manifests  itself.  For  careful  measurements  to 
locate  the  trouble,  the  wire  chief  at  the  nearest 
large  testing  office  should  be  called  upon.  The 
method  of  making  these  tests  is  fully  described  in 
Chapter  XX. 

To  facilitate  testing,  two  or  more  of  the  jacks 
may  be  wired  to  binding  posts  suitably  located  for 
this  purpose.  The  desired  connection  with  the  test 
circuit  can  then  be  made  by  means  of  patching  cords. 


FIG.  131.  —  Western 
Electric  Company's 
Forty-one  Wire  Toll 
Test  Panel  Exten- 
sion. 


FIG.  132.  —  Simplex  Wiring  for  Small  Toll  Test  Panel. 


A  very  convenient  arrangement  is  a  shelf  or  table  just  below  the  panel, 
on  which  the  testing  instruments  and  patching  cords  may  be  placed. 


CHAPTER  XVII 
LINE   CONSTRUCTION 

Introduction.  —  In  a  toll  system  the  outside  plant  usually  repre- 
sents three-quarters  of  the  total  investment,  at  leasjt,  and  its  correct 
design  from  an  engineering  standpoint  is  correspondingly  important. 
There  are  few  more  intricate  problems  than  those  which  arise  here, 
involving  the  determination  of  correct  proportions  electrically  and 
mechanically  and  an  economical  layout  of  routes.  The  quality  of 
service  depends  not  only  upon  correct  design  and  good  construction, 
but  it  is  affected  afterwards  by  the  maintenance.  Low  costs  in  the 
last  respect  depend  in  turn  upon  the  essentials  for  good  service  at 
the  outset. 

Construction  standards  have  been  advancing  year  by  year,  as  a 
whole,  and  the  present  tendency  is  happily  toward  the  policy  that 
the  best  is  none  too  good.  The  great  need  of  stoutly  built  lines 
throughout  those  parts  of  the  country  subject  to  sleet  storms  has 
been  learned  from  experience.  Reliability  is  one  of  the  well  recog- 
nized elements  of  good  service  and  should  be  taken  into  due  account 
in  mechanical  design. 

Toll-line  construction  at  the  present  time  falls  in  one  of  two  general 
classes  or  types,  aerial  open- wire  and  underground  cable.  The  former 
meets  the  requirements  of  long  lines  with  a  limited  number  of  circuits, 
from  an  economic  standpoint.  It  is  greatly  desirable  to  adopt  the 
second,  or  underground  type,  however,  when  it  does  not  produce  exces- 
sive circuit  charges,  for  the  obvious  advantage  of  greater  reliability. 
Short  toll  lines  connecting  a  city  with  its  suburbs,  or  two  adjacent 
cities,  are  usually  underground  as  a  matter  of  course.  In  these  cases 
the  ducts  employed  are  usually  part  of  a  general  underground  system. 

The  cost  of  underground  construction  is  prohibitive  for  toll  lines 
carrying  few  circuits,  especially  the  circuits  for  very  long  haul  busi- 
ness. It  was  prohibitive  in  any  case  for  circuits  even  of  moderate 
length  before  the  art  of  loading  was  developed.  But  since  that  event 
it  has  been  found  economical  to  place  a  few  of  the  very  large  trunk 

"  245 


246  TOLL  TELEPHONE  PRACTICE 

lines  in  underground  loaded  cables.  Such  lines  now  connect  New  York 
and  Philadelphia,  New  York  and  New  Haven,  and  Chicago  and  Mil- 
waukee. It  is  planned  to  extend  the  Philadelphia  line  to  Baltimore 
and  Washington  and  the  New  Haven  line  to  Providence  and  Boston. 
In  each  instance  these  cables  contain  more  circuits  than  could  be 
sustained  by  a  single  pole  line. 

Except  in  rural  districts  toll  lines  are  always  metallic  and  the  maxi- 
mum capacity  of  the  standard  pole  line  of  forty  wires  is  therefore 
twenty  circuits.  Such  lines  have  sometimes  been  overloaded  and 
their  capacity  increased  25  per  cent,  or  at  the  most  50  per  cent,  but 
this  is  attended  with  disadvantage  from  the  standpoint  of  uninter- 
rupted service. 

The  choice  of  pole-line  routes  is  a  most  important  matter  and  should 
receive  careful  study.  The  large  telegraph  companies  have  adopted 
rights-of-way  on  steam  railroads  to  a  great  extent,  partly  for  com- 
mercial reasons.  The  long-distance  telephone  companies  have  gen- 
erally followed  the  policy  of  selecting  country  highways,  one  of  the 
prominent  reasons  for  which  is  the  higher  insulation  which  can  be 
maintained. 

In  choosing  a  highway  route  between  two  given  points  it  is  usually 
possible  to  find  a  number  of  alternate  routes  which  are  feasible.  The 
shortest  route  is  generally  the  most  economical  one,  but  this  cannot 
be  settled  finally  until  the  total  cost,  including  right-of-way,  is  esti- 
mated for  each  of  the  feasible  routes.  Preliminary  to  choosing  a 
route,  the  country  is  driven  over  by  an  experienced  locator,  with  a 
right-of-way  agent,  and  the  general  conditions  are  carefully  observed. 
Then  the  feasible  routes  are  laid  out  accurately  on  a  map  and  the 
cost  of  each  route  is  determined  as  nearly  as  possible. 

Private  right-of-way  is  usually  undesirable,  because  it  is  more 
expensive  to  distribute  material,  and  more  expensive  afterwards  to 
maintain  the  line.  At  the  same  time,  where  such  routes  will  save 
long  detours  by  highway,  or  avoid  difficult  obstacles,  they  may  be 
the  better  choice. 

The  legal  title  to  a  right-of-way  should  always  be  made  secure  by 
obtaining  the  proper  consents  from  the  authorities  and  the  property 
owners.  This  will  save  much  future  expense  from  changes  in  location 
and  damage  suits,  and  perhaps  from  the  attempts  of  other  companies 
to  overbuild  or  underbuild  along  the  same  route.  At  the  same  time 
the  necessary  trimming  rights  should  be  secured,  not  only  to  clear 


LINE  CONSTRUCTION  247 

the  line  of  foliage  when  built,  but  to  keep  it  clear  afterward  as  a  matter 
of  maintenance. 

The  Line.  —  The  properties  of  telephone  lines  have  been  extensively 
treated  in  another  chapter,  but  it  is  essential  to  keep  certain  features 
in  mind  from  a  construction  standpoint.  High  efficiency  of  trans- 
mission with  uniform  (unloaded)  lines  of  open  wire  depends  on  low 
resistance,  low  capacity  and  high  insulation;  it  depends  also  on  a 
practically  perfect  balance  between  the  two  sides  of  a  metallic  circuit, 
which  should  be  alike  in  resistance,  capacity  and  insulation. 

These  facts  should  be  kept  clearly  in  mind  in  line  building.  Metal- 
lic pairs  should  always  consist  of  the  same  size  and  kind  of  wire  and 
the  joints  should  be  looked  after  with  the  utmost  care.  The  insula- 
tion should  be  attended  to  with  the  same  care  and  only  perfectly  whole 
insulators  should  ever  be  used.  The  trimming  should  be  followed  up 
carefully  and  all  guys  should  clear  the  line  wires  by  a  safe  distance. 

Transpositions  are  usually  cut  in  after  the  wires  are  strung,  pulled 
up  and  tied  in.  They  should  never  be  cut  in,  however,  until  the  line 
has  been  carefully  measured  and  the  transposition  poles  accurately 
located  and  marked. 

When  stringing  additional  circuits  the  transpositions  can  sometimes 
be  cut  in  conveniently  as  the  wire  is  strung,  thus  avoiding  extra  cuts 
and  joints.  But  as  a  rule  it  is  best  to  proceed  with  only  one  operation 
at  a  time. 

As  fast  as  the  line  is  completed  it  ought  to  be  carefully  inspected 
for  faults  of  every  kind,  before  the  crew  is  too  far  away  to  make  altera- 
tions economically.  The  matter  of  inspection  is  most  important  and 
pays  for  itself  in  many  ways,  especially  when  the  crews  are  under 
pressure  to  hold  the  unit  costs  down  to  a  minimum. 

There  is  little  more  to  be  said  from  an  electrical  standpoint  as  it 
concerns  construction,  aside  from  what  follows  in  relation  to  the  prop- 
erties of  line  wire.  The  mechanical  features  of  line  construction  are 
fully  taken  up  in  the  succeeding  portions  of  the  present  chapter. 

Line  Wire.  —  The  only  wire  that  should  be  used  in  the  construction 
of  toll  lines,  especially  the  long  lines,  is  hard-drawn  copper.  It  is 
true,  of  course,  that  for  short  branches  and  sometimes  for  a  main  line 
of  medium  length,  say  one  hundred  fifty  miles,  Extra  Best  Best  iron 
wire  can  be  used.  However,  due  to  the  intrinsic  value  of  copper  and 
its  property  of  resisting  corrosion,  it  should  always  be  used  unless 
special  conditions  make  iron  more  economical. 


248  TOLL  TELEPHONE  PRACTICE 

The  intrinsic  value  of  copper  remains  the  same,  on  the  average, 
even  after  it  has  been  in  use  for  years.  During  the  past  few  years 
when  the  price  was  continually  fluctuating,  it  frequently  happened 
that  a  telephone  company,  by  closely  following  the  market  and  pur- 
chasing at  greatest  advantage,  could  buy  line  wire  and  after  six  months' 
or  a  year's  use  find  its  value  enhanced  considerably  —  perhaps  20  per 
cent  or  more. 

It  hardly  seems  necessary  to  add  that  the  inferior  grades  of  iron 
wire,  such  as  Best  Best  and  steel,  should  never  be  used  except  for 
very  short  distances  where  an  extremely  long  span  is  unavoidable, 
where  conductivity  must  be  sacrificed  for  tensile  strength.  By  ten- 
sile strength  is  meant  the  ability  to  resist  a  direct  pulling  stress  and 
this  is  usually  stated  as  the  ultimate  strength  or  the  pulling  stress  in 
pounds  required  to  break  the  wire.  Good  hard-drawn  copper  wire 
has  a  tensile  strength  equal  at  least  to  three  times  its  own  weight  in 
pounds  per  mile;  and  in  drawing  specifications  for  such  wire  a  clause 
stipulating  this  degree  of  strength  is  usually  inserted.  Of  course  the 
most  important  electrical  property  of  a  conductor  is  its  conductivity 
or  conductance.  A  conductor  whose  resistance  is  r  ohms  has  a  con- 
ductance equal  to  - ,  i.e.,  the  conductance  varies  inversely  with  the 

resistance;  and  since  the  resistance  varies  directly  with  the  cross 
section  of  the  conductor,  the  conductance  must  vary  inversely  with 
the  cross  section.  Thus  an  iron  wire  having  about  six  times  the 
cross  sectional  area  of  a  given  copper  wire  would  equal  the  latter  in 
resistance;  but  the  additional  cross  section  of  the  iron  wire  would 
increase  the  distributed  capacity  of  the  line  and  impair  its  efficiency. 
Besides  this,  the  additional  weight  of  the  iron  wire  would  so  increase 
the  strain  on  pins,  cross-arms  and  poles,  as  to  call  for  much  heavier 
construction  throughout,  at  greatly  increased  cost. 

A  most  convenient  method  of  comparing  the  conductivity  of  wires, 
regardless  of  their  size,  is  the  mile-ohm,  or  more  properly,  the  weight 
per  mile-ohm.  The  weight  per  mile-ohm,  as  the  words  clearly  indicate, 
is  the  weight  of  a  circular  wire  one  mile  long  and  of  such  a  cross  section 
as  to  have  a  resistance  of  one  ohm.  Naturally  the  value  of  the  mile- 
ohm  will  decrease  as  the  conductivity  of  the  metal  increases;  or  in 
other  words,  the  conductivity  varies  inversely  with  the  weight  per 
mile-ohm.  Obviously  the  mile-ohm  equals  the  weight  per  mile  mul- 
tiplied by  the  resistance  per  mile.  The  conductivities  of  two  metals 


LINE  CONSTRUCTION  249 

can  be  readily  compared  if  the  weight  per  mile-ohm  of  each  is  known. 
Thus  if  the  weight  per  mile-ohm  of  pure  annealed  copper  is  859  and 
that  of  a  sample  is  900,  the  percentage  of  conductivity  X  of  the  sam- 
ple, taking  pure  copper  as  a  standard,  is  then  determined  from  the 
proportion 

X  :  100  ::  859  :  900. 

IPO  X  859  _  ~ 

-j^-      -95-44/0. 

From  the  formula  that  the  mile-ohm  equals  weight -per  mile  times 
resistance  per  mile,  we  can  obtain  any  one  of  the  three  quantities  if 
the  other  two  are  known.  Thus  the  resistance  per  mile  equals  the 
mile-ohm  divided  by  weight  per  mile,  and  the  weight  per  mile  equals 
the  mile-ohm  divided  by  resistance  per  mile. 

As  previously  stated,  copper  is  the  best  conductor  for  long  toll  lines, 
because  no  other  material  gives  so  good  a  combination  of  tensile 
strength  and  conductivity.  The  tensile  strength  of  annealed  copper 
is  about  34,000  pounds  per  square  inch,  and  this  figure  is  raised  by 
hard  drawing  to  60,000  or  even  70,000  pounds  per  square  inch,  with 
a  corresponding  increase  in  the  resistance  of  only  2  per  cent  to  4  per 
cent.  The  copper  line  wire  should  be  free  from  flaws,  seams,  scale 
and  all  other  mechanical  imperfections,  and  should  be  cylindrical 
in  form  and  within  one  and  one-half  mils  of  the  nominal  gauge.  The 
following  are  specifications  submitted  to  the  manufacturers  who  fur- 
nish copper  wire  for  the  largest  toll-line  companies  in  the  United 
States. 

"  Specification  for  Line  Wire.  —  The  standard  line  wire  shall  be  of  hard- 
drawn  copper  and  shall  conform  to  the  following  specifications: 

"  The  quality  of  copper  used,  the  method  of  manufacture,  and  the  method  of 
handling  and  shipment  of  the  wire  shall  be  such  as  to  insure  for  the 
wire  the  mechanical  and  electrical  properties  and  the  finish  called  for 
in  these  specifications.  The  quality  of  the  copper  used,  the  electrical 
and  mechanical  properties  and  the  finish  of  the  wire  must  be  deter- 
mined by  the  manufacturer  before  the  wire  is  delivered.  The  telephone 
company  is  to  have  the  right  to  make  such  tests  as  it  may  desire  of  the 
quality  of  the  copper  used,  of  the  electrical  and  mechanical  properties 
and  finish  of  the  wire  at  any  time,  before,  during,  or  after  the  process 
of  manufacture,  and  to  have  an  inspector  of  its  own  witness  the  whole 
or  any  portion  of  the  manufacture,  handling,  or  shipment  of  the  wire. 
The  inspector  of  the  telephone  company  is  to  have  the  power  to  reject 
any  of  the  material  or  finished  wire  which  the  herein  required  tests 


250  TOLL  TELEPHONE  PRACTICE 

show  to  be  defective  in  any  way.  The  inspection  of  the  copper  used, 
and  of  the  process  of  manufacture  shall,  however,  not  relieve  the  manu- 
facturer from  the  obligation  of  furnishing  perfect  material,  and  sound 
and  reliable  work;  and  any  imperfect  material,  or  unfaithful  work,  that 
may  be  discovered  before  the  final  acceptance  of  the  wire  shall  be 
corrected  immediately  upon  the  requirement  of  the  telephone  company, 
notwithstanding  that  it  may  have  been  overlooked  by  the  inspector. 
If  upon  test  it  be  found  by  the  telephone  company  that  the  require- 
ments for  the  wire,  or  for  the  finish,  are  not  fulfilled  when  the  wire  is 
offered  for  final  acceptance,  the  expense  of  all  tests  made  by  the  tele- 
phone company  on  such  defective  wire  shall  be  borne  by  the  manu- 
facturer. 

"  Manufacture.  —  The  copper  bars  before  rolling  shall  be  entirely  free  from 
defects.  Each  coil  shall  be  drawn  in  one  continuous  length  and  shall 
be  free  from  factory  joints. 

"  Finish.  —  The  wire  shall  be  uniformly  cylindrical  in  form  and  free  from 
scales,  inequalities,  flaws,  splints  and  all  other  imperfections. 

Mechanical  and  Electrical  Requirements 

11  The  weight  in  pounds  per  mile  is  found  by  multiplying  the  square  of  the 
diameter  of  the  wire  in  inches  by  the  constant  number  16,030. 

"  Coils.  —  Unless  otherwise  specified  by  the  telephone  company,  the  weights 

of  the  coils  shall  lie  within  the  limits  given  in  Table  i. 
"  The  diameter  of  the  eye  of  the  coil  shall,  in  every  case,  be  not  less  than 
20  inches  nor  more  than  22  inches. 

"  Packing  for  Shipment.  —  Each  coil  shall  be  securely  bound  with  at  least 
four  separate  pieces  of  strong  twine,  and  shall  be  so  protected  by  wrap- 
pings of  burlap,  that  there  will  be  no  danger  of  mechanical  injury  to 
the  coil  during  transportation.  These  wrappings  of  burlap  must  be 
placed  upon  the  coil  after  it  has  been  secured,  as  specified  above,  by  the 
twine.  Each  coil  shall  have  its  weight  and  length  of  wire  plainly  and 
indelibly  marked  on  two  strong  tags.  One  of  these  tags  shall  be  attached 
to  the  coil  outside  of  the  burlap. 

"  Testing  Apparatus.  —  All  tests  must  be  made  with  apparatus  satisfactory 
to  the  telephone  company." 

In  this  connection  it  might  be  well  to  add  a  few  remarks  regarding 
standard  sizes  in  which  wire  is  drawn.  The  Birmingham  Wire  Gauge, 
abbreviated  B.  W.  G.,  is  more  commonly  used  for  iron  wire,  while 
the  Brown  and  Sharpe  Gauge,  abbreviated  B.  &  S.  and  the  New 
British  Standard  Gauge,  N.  B.  S.  G.,  are  most  frequently  used  for 
copper  wire.  A  few  well-known  relations  between  the  wire  sizes  in 
the  B.  &  S.  gauge  will  be  appended,  as  they  afford  a  ready  means  of 
remembering  the  entire  table.  The  diameter  of  the  wire  is  expressed 


M 

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LINE  CONSTRUCTION 


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251 


252 


TOLL  TELEPHONE  PRACTICE 


in  mils,  or  one-thousandths  of  an  inch,  and  the  area  of  the  cross  section 
is  expressed  in  circular  mils,  which  for  any  given  size  of  wire  is  the 
square  of  the  diameter.  The  area  may  also  be  expressed  in  square 
mils,  which  gives  the  true  area  in  thousandths  of  a  square  inch  and 
equal  the  square  of  the  diameter  in  mils,  times  0.7854.  It  may  be 
well  to  bear  in  mind  that  the  circular  mil  is  to  the  square  mil  as  the 
circle  is  to  the  square  in  which  it  is  inscribed;  and,  consequently, 
the  number  of  circular  mils  in  a  given  area  is  always  greater  than 
the  number  of  square  mils. 

Regarding  the  relation  between  the  different  sizes  of  wire  in  the 
B.  &  S.  table,  it  may  be  noted  that  a  wire  which  is  three  sizes  larger 
than  another  will  have  twice  the  weight  and  one-half  the  resistance, 
and  a  wire  which  is  ten  sizes  larger  than  another  will  be  ten  times  as 
heavy  and  have  one-tenth  the  resistance.  Then  by  knowing  the 
above  relation  and  remembering  that  No.  10  B.  &  S.  wire  is  approxi- 
mately one-tenth  of  an  inch  in  diameter  and  has  a  resistance  of  one 

TABLE  2 

BROWN  AND  SHARPE  WIRE  GAUGE 


B.&S. 
Gauge. 

Diameter 
in  Mils. 

Area  in 
Circular 
Mils. 

Weight  in 
Pounds  per 
1000  Feet. 

Tensile  Strength. 

Feet  per 
Pound  of 
Copper. 

Ohms  per 
1000  Feet 
at68°F. 
Hard-drawn. 

Hard- 
drawn. 

Annealed. 

0 

32S 

105,534 

3I9-4 

4973 

2819 

3-13 

•  10033 

I 

.'89 

83,694 

253-3 

3943 

2234 

3-95 

.  12649 

2 

258 

66,373 

200.9 

3127 

1772 

4-99 

•15953 

3 

229 

52,634 

159-3 

2480 

1405 

6.29 

.20114 

4 

204 

4i,743 

126.3 

1967 

1114 

7-93 

-25361 

5 

182 

33,102 

IOO.2 

1560 

884 

IO.OO 

-31987 

6 

162 

26,250 

79-4 

1237 

700 

12.  6l 

-  40332 

7 

144 

20,820 

63.01 

980 

555 

15.90 

-  50854 

8 

128 

16,510 

49-97 

778 

-440 

20.05 

.64127 

9 

114 

13,092 

39-64 

617 

349 

25.28 

.80876 

10 

IO2 

10,384 

3I-42 

489 

277 

31-38 

1.0199 

ii 

90.7 

8,234 

24.92 

388 

219 

40.  20 

1.2854 

12 

80.8 

6,530 

19.8  . 

307 

174 

50.69 

1.6218 

13 

72.0. 

5,i78 

15-7 

244 

138 

63.91 

2  .  0443 

14 

64.1 

4,107 

12.4 

193 

109 

80.59 

2-5779 

ohm  and  a  weight  of  thirty-two  pounds  per  thousand  feet,  the  whole 
table  can  be  constructed  mentally  with  sufficient  accuracy  for  practical 
purposes.  An  additional  relation  which  should  be  remembered  is 
that  the  number  of  feet  per  ohm  can  be  ascertained  by  dropping  one 
cipher  from  the  number  expressing  the  circular  mils  in  the  conductor; 


LINE  CONSTRUCTION  253 

also  that  the  weight  may  be  ascertained  by  dropping  four  ciphers 
from  the  number  of  circular  mils  and  multiplying  by  the  weight  of 
No.  10  B.  &  S.  wire.1 

Table  2  gives  the  number,  the  area  in  circular  mils,  the  weight  in 
pounds,  the  tensile  strength  and  the  resistance  in  ohms  per  thousand 
feet  in  the  B.  &  S.  gauge. 

Spans.  —  As  already  stated,  copper  wire  when  hard-drawn  has  a 
tensile  strength  of  about  60,000  pounds  per  square  inch  and  an  elastic 
limit  of  about  30,000  pounds.  These  values  represent  the  ultimate 
and  should  never  be  used  in  determining  the  proportions  of  a  line. 
The  actual  strength  of  any  size  of  wire,  as  given  in  Table  2,  should 
always  be  divided  by  a  proper  factor  of  safety. 

The  several  factors  which  determine  the  stresses  in  wire  spans  are 
the  length  of  span,  initial  sag  at  the  center  of  the  span,  changes  of 
temperature,  weight  of  the  conductor  and  external  loads  of  wind, 
sleet  and  snow.  The  stresses  caused  by  external  loads  are  often  very 
formidable  and  frequently  cause  great  triable,  due  to  the  fact  that 
they  are  not  sufficiently  considered  in  the  design  of  the  line. 

It  is  a  fundamental  principle  of  mechanics  that  a  uniform  wire 
which  is  freely  suspended  between  two  supports,  will  assume  a  curve 


B  .  ,,-  :•-< 

FIG.  133 

technically  known  as  the  catenary,  when  equilibrium  is  established. 
However,  the  exact  determination  of  the  stresses  by  means  of  this 
curve  is  not  convenient;  but  in  the  case  under  consideration,  the 
parabola,  a  much  simpler  curve,  closely  approximates  the  catenary, 
and  will  be  used  in  the  following  deductions.  The  parabola  is  the 
curve  that  is  assumed  by  a  cord  of  no  weight,  under  equilibrium, 
when  loaded  with  an  infinite  number  of  infinitely  small  equal  weights, 
which  are  uniformly  distributed  horizontally.  Then,  referring  to 
Fig.  133,  if  a  wire  is  suspended  between  the  points  A  and  C,  it  will 
take  the  curve  ABC.  What  must  now  be  determined  is  the  relation 

1  "  How  To  Remember  the  Wire  Table,"  by  Chas.  F.  Scott,  in  the  Electric  Journal, 
April,  1905. 


254  TOLL   TELEPHONE  PRACTICE 

between  AC,  or  the  length  of  the  span  which  we  shall  call  L,  the 
vertical  deflection  d  at  the  middle  point  of  the  span,  the  horizontal 
tension  on  the  wire  at  the  center  of  the  span  and  the  weight  of  the 
wire  per  foot.  This  relation  can  be  expressed  as  follows: 


or 

,      Ih»  /  s 

d=—,....    ,   ,    .    .    .     (2) 

in  which  L  is  the  length  of  the  span  in  feet,  d  is  the  central  deflection 
in  feet,  T  is  the  tension  on  the  wire  at  the  center  of  the  span  in  pounds, 
and  w  the  weight  of  the  wire  in  pounds  per  foot. 

The  stress  at  any  other  point  than  the  center  of  the  span  equals  the 
stress  at  the  center  plus  the  weight  of  a  length  of  wire  equal  to  the 
perpendicular  distance  from  that  point  to  the  lowest  point  of  the  wire 
in  the  span.  Thus  the  stress  at  the  supports  A  and  C  equals  a 
Tg  =  T  +  dw.  The  quantity  dw  for  ordinary  spans  is  negligible  and, 
consequently,  has  been  disregarded  because  of  the  complication  it 
would  introduce  in  the  formula. 

From  equations  (i)  and  (2)  it  will  be  noted  that  for  a  given  wire 
and  span  the  tension  varies  inversely  as  the  deflection,  and  that  for 
a  given  tension  and  wire,  the  deflection  varies  directly  with  the  square 
of  the  span;  hence  the  strain  on  the  wire  can  be  reduced  either  by 
shortening  the  span  or  by  increasing  the  deflection.  To  give  a  concrete 
example,  we  shall  consider  the  case  of  a  No.  8  B.  &  S.  copper  line  on 
poles  that  are  spaced  at  130  feet,  or  approximately  forty  to  the  mile. 
Then  what  must  be  the  deflection,  assuming  a  factor  of  safety  of  four  ? 
This  means  that  the  tension  T  in  the  above  formula  should  not  exceed 
one-quarter  of  the  breaking  strain  of  the  wire,  which  from  the  table 
gives  a  maximum  value  of  194  pounds.  Using  this  value  of  T  as  a 
basis,  we  shall  now  determine  from  formula  (2)  what  the  minimum 
deflection  at  the  center  of  the  span  should  be.  Then,  proceeding 
upon  the  assumption  that  the  wire  has  been  given  the  calculated 
deflection,  we  shall  further  assume  a  most  severe  temperature  varia- 
tion in  combination  with  external  forces  which  are  but  seldom  met, 
but  which,  nevertheless,  are  a  possibility,  especially  in  northern 
climates.  This  calculation  is  given  in  order  to  show  the  great  neces- 
sity of  a  proper  consideration  of  the  natural  forces,  such  as  wind  and 


LINE  CONSTRUCTION  255 

sleet,  in  the  design  of  toll  lines,  if  they  are  to  be  proof  against  the 
ravages  of  a  severe  winter.  Having  assumed  our  value  of  T  we  now 
find  the  weight  of  the  wire,  from  the  table,  to  equal  .049  pound  per 
foot.  Then  if  we  substitute  these  values  in  equation  (2),  we  have 

,      i3o2  X  .049  ,  ,       .     , 

a  =  -~  —         -  =  0.534  foot  =  6.41  niches. 
8  X  194 

This  minimum  deflection  should  never  be  exceeded  and,  conse- 
quently, must  correspond  to  the  lowest  temperature  which  can  be 
expected.  The  deflection  given  to  a  line  at  a  stated  temperature 
must  be  so  great  that  when  the  wire  contracts  in  cold  weather,  the 
resultant  deflection  will  not  be  less  than  the  minimum.  To  ascertain 
the  deflection  required  at  some  given  temperature,  within  specified 
temperature  limits,  we  must  determine  the  length  of  the  wire  in  the 
span  at  the  time  of  erection  and  also  for  the  lowest  probable  tempera- 
ture. The  total  length  of  the  wire  in  the  span  is  approximately 


........  (3) 

3  *• 

from  which  the  value  of 


d  = 


in  which  U  is  the  actual  length  of  the  wire  and  L  the  length  of  the 
span.  Then  if  we  take  the  coefficient  of  expansion  of  copper,  per 
degree  F.,  as  0.000,009,3  of  its  length  we  can  readily  determine  the 
actual  length  of  the  wire  in  a  span  at  any  temperature. 

If  we  assume  in  the  previous  example  that  the  wire  was  erected  at 
90°  and  that  the  minimum  temperature  to  which  it  will  be  exposed 
is  —10°  F.,  then  a  sufficient  deflection  must  be  allowed  at  90°  to 
bring  the  deflection  at  —  10°  to  the  minimum  value  just  obtained. 
The  length  of  the  wire  at  —  10°  F.  is  obtained  from  equation  (3). 

,  8  X  (o.534)2 
L!  =  130  H  --  v    D^    =  130.0. 

This  would  be  increased  at  90°  F.,  or  for  a  temperature  variation  of 
100°  F.,  to  130.0  X  .000,009,3  x  I00>  this  giving  a  length  at  the 
higher  temperature  of  130.0  +  (130.0  X  .000,009,3  X  100)  or  130.121 
feet.  The  required  deflection  for  this  length  can  now  be  determined 
by  equation  (4),  or 


j          7390  X  (130.121  —  130)  ,  .     , 

d  =  i/** L-i2— *-*  =  2.43  feet  =  29.2  inches, 

T  5 


256 


TOLL  TELEPHONE  PRACTICE 


The  comparison  of  the  deflection  just  calculated  with  the  previous 
deflection  of  6.41  inches  shows  that  a  large  temperature  allowance 
should  be  made.  However,  in  practice,  the  changes  in  deflection 
due  to  temperature  changes  are  found  not  to  correspond  exactly  with 
the  law  of  expansion,  because  of  elastic  stretching  under  tension. 
This  partly  offsets  the  changes  in  length  due  to  temperature,  thereby 
lessening  the  changes  in  deflection.  The  actual  behavior  of  copper 
wire,  when  erected  under  various  tensions,  has  never  been  exhaustively 
determined;  but  it  is  safe  to  assume  that  the  effective  coefficient  of 
expansion  is  subject  to  considerable  variation,  and  a  value  of  0.000,004 
instead  of  0.000,009,3  is  probably  a  fair  approximation.  In  Table  3 
are  the  temperature  effects  in  spans  as  given  in  Roebling's  handbook. 

TABLE  3 

TEMPERATURE  EFFECTS  IN  SPANS  OF  HARD-DRAWN  COPPER  WIRE 


Spans  in 
Feet. 

Deflections  in  Inches  for  Different  Temperatures  —  Fahrenheit. 

—  10° 

30° 

40° 

50° 

60° 

70° 

80° 

90° 

100° 

SO 

•5 

6 

8 

9 

9 

IO 

ii 

n 

12 

60 

•7 

8 

IO 

ii 

ii 

12 

13 

13 

14 

70 

I.O 

10 

II 

12 

13 

14 

*S 

IS 

J7 

80 

1.2 

ii 

13 

14 

15 

16 

17 

18 

19 

90 

1.6 

r3 

14 

16 

17 

18 

19 

20 

21 

IOO 

1.9 

14 

16 

17 

19 

20 

21 

23 

24 

no 

2.3 

16 

18 

19 

21 

22 

24 

25 

26 

120 

2.8 

17 

19 

21 

22 

24 

26 

27 

28 

130 

3-2 

19 

21 

23 

25 

26 

28 

29 

31 

140 

3-7 

20 

23 

25 

27 

28 

3° 

32 

33 

150 

4-3 

22 

24 

26 

28 

30 

32 

34 

36 

160 

4-9 

23 

26 

28 

3° 

32 

34  ' 

36 

38 

170 

5-5 

25 

28 

30 

32 

35 

37 

38 

40 

180 

6.2 

26 

29 

32 

34 

37 

39 

4i 

43 

190 

7.0 

28 

31 

34 

36 

39 

4i 

43 

45 

200 

7-7 

31 

33 

36 

38 

4i 

43 

45 

48 

s  It  will  be  noted  that  the  deflections  at  — 10°  F.,  in  this  table,  are 
based  on  a  stress  of  30,000  pounds  per  square  inch,  thus  utilizing  a 
factor  of  safety  of  two ;  and  as  the  safety  factor  used  in  our  calculation 
is  four,  the  calculated  deflection  at  — 10°  is  approximately  twice  as 
great  as  that  given  in  the  table. 

In  our  calculation  thus  far  we  have  taken  care  of  the  weight  of  the 
wire  itself,  but  we  have  not  considered  any  of  the  external  forces  to 
which  it  is  exposed.  These  manifest  themselves  in  additional  weight 


LINE  CONSTRUCTION  257 

caused  by  a  coating  of  sleet  on  the  wire,  and  in  wind  pressure  on  the 
bare  or  ice-covered  surface  of  the  wire. 

We  shall  consequently  assume  that  our  line  has  become  coated  with 
ice  to  a  thickness  of  three-eighths  of  an  inch,  which  is  quite  common 
during  severe  weather  in  many  localities.  Fig.  134  is  a  photograph 
of  a  piece  of  ice-coated  wire  taken  from  a  line  near  Winona,  Minne- 


FIG.  134.  —  Illustration  of  Ice-coated  Wire. 

sota.  This  line  was  exposed  to  a  sleet  storm  on  Jan.  28,  1909,  which 
resulted  in  the  sleet  formation  shown  ;  this  measured  i\  by  4^  inches. 
This  shows  the  possibilities  of  sleet  formation  and  indicates  that  a 
three-eighths  inch  formation  is  not  an  abnormal  condition.  A  layer 
of  ice  three-eighths  of  an  inch  in  thickness  would  weigh  0.237  pound 
per  linear  foot,  which  is  approximately  five  times  the  weight  of  the 
wire  itself,  and  would  increase  the  stresses  severely.  Assuming  this 
load  at  the  minimum  temperature  of  —  10°,  for  which  the  calculated 
deflection  is  0.534  foot,  we  can  obtain  the  tension  at  the  center  of  the 
span  from  equation  (i),  or 


_  (130)'  X  (0.237  +     -          =  II30pounds. 
8  X  0.534 


258 


TOLL  TELEPHONE  PRACTICE 


This  stress  is  354  pounds  greater  than  the  ultimate  tensile  strength 
of  the  wire  as  given  in  the  table  and  the  wire  would  consequently 

stretch  or  break.  Due  to  the  fact 
that  this  ice  load  is  often  neg- 
lected, many  telephone  companies 
suffer  severely  in  sleet  storms  even 
of  moderate  severity.  The  proper 
remedy  is  larger  deflections,  shorter 
spans,  or  stronger  conductors; 
otherwise  such  conditions  as  those 
shown  in  Fig.  135  are  unavoidable. 
In  addition  to  the  ice  load  we 
have  the  wind  pressure  to  consider. 
This  pressure  may  be  considered 
as  acting  at  right  angles  to  the 
weight  of  the  wire,  and  its  com- 
ponent of  downward  pressure  fre- 
quently increases  very  considerably 
the  resulting  total  stress.  The  pressure  P  to  which  the  line  wire  is 
exposed  may  be  expressed  by  the  equation 

P  =  o.o$pD,     ....     ....     (5) 

in  which  p  is  the  normal  pressure  of  the  wind  in  pounds  per  square 
foot  and  D  the  diameter  of  the  wire  in  inches.  The  pressure  p  may 
vary  from  a  few  ounces  per  square  foot  in  a  moderate  breeze  to  from 
30  to  40  pounds  per  square  foot  in  a  hurricane.  We  shall  now  assume 
that  a  No.  8  B.  &  S.  wire  is  subject  to  the  maximum  pressure  of  40 
pounds  per  square  foot,  when  the  pressure  p  from  the  above  formula  is 

0.05  X  40  X  0.128  =  0.256  pound. 

This  pressure  is  exerted  at  right  angles  to  the  weight  of  the  wire  and, 
consequently,  the  resulting  stress  is 


FIG.  135.  —  Effect  of  Ice  Formation  on 
Line  Wire. 


W 


+  p2  =  v  (0.049)2  -I-  (0.256)2  =  0.261  pound. 

Substituting  this  value  of  W,  0.261,  for  W  in  equation  (i),  gives  the 
tension  on  the  wire  under  the  assumed  conditions  of  wind  pressure  of 
40  pounds  per  square  foot  and  a  deflection  of  0.534  foot.  Thus 

~      (130)2  X  0.261 

*  =  N  ^   =  1033  pounds. 

8  X  0.534 


LINE  CONSTRUCTION  259 

This  stress  is  obviously  more  than  the  wire  can  stand  without  stretch- 
ing or  breaking,  because  it  is  257  pounds  greater  than  the  breaking 
weight.  In  this  calculation  the  wire  was  subjected  to  a  wind  load 
without  sleet,  and  even  then  the  stress  was  shown  to  be  dangerous. 
Assuming  now  but  half  the  wind  pressure,  or  20  pounds  per  square 
foot,  in  combination  with  the  previous  sleet  load,  it  is  evident  that 
the  result  would  be  disastrous,  for  in  this  case  Z>,  the  diameter  of  the 
wire,  is  0.878  inch.  Then 

P  =  0.05  X  20  X  0.878  =  0.878  pound, 
and  / 

W  =  V(o.286)2  +  (0.878)2  =  0.923  pound. 

By  substituting  in  equation  (i), 

^      (i3o)2  X  0.023 

T  =  ^-   *•*  =  3650  pounds. 

8  X  0.534 

This  tension  is  nearly  five  times  the  breaking  weight  of  the  wire, 
which  would  consequently  give  way  long  before  conditions  as  severe 
as  those  assumed  have  been  reached.  This  shows  that  if  the  line  is 
exposed  to  very  severe  conditions,  similar  to  those  assumed,  a  large 
initial  factor  of  safety  is  necessary  to  insure  uninterrupted  service. 
It  must  be  remembered,  however,  that  in  these  calculations  the  sup- 
ports were  assumed  to  be  perfectly  rigid  under  all  conditions  of  stress 
and  the  wire  to  be  inelastic.  This,  of  course,  is  never  true  in  practice, 
as  all  material  is  more  or  less  elastic,  and  the  occasional  changes  in 
direction  of  a  line  relieve  the  stresses  somewhat  by  bending  of  the 
supports.  The  standard  practice  of  the  American  Telephone  and 
Telegraph  Company  in  this  respect  is  as  follows: 

"  Sag  of  Wires.  —  The  wire  shall  be  strung  with  a  uniform  sag  so  that  all 
the  wires  on  each  cross-arm  shall  be  even  and  level,  except  where  No.  14 
N.  B.  S.  G.  wires  are  on  the  same  arm  with  No.  8  B.  W.  G.  or  No.  12 
N.  B.  S.  G.  wires. 

"  The  sag  for  No.  8  and  No.  12  wires  shall  be  as  given  in  Table  4,  making 
the  allowance  therein  indicated  for  temperature  and  length  of  span. 

"  The  sag  for  No.  14  N.  B.  S.  G.  wires  shall  be  at  least  two  inches  greater 
than  that  indicated  in  Table  4  for  the  same  temperature  and  spans." 

The  deflections  given  in  Table  4  apply  to  the  entire  plant  of  the 
American  Telephone  and  Telegraph  Company.  Both  theory  and  ex- 
perience show  that  these  deflections  are  inadequate  for  severe  condi- 
tions, such  as  heavy  sleet  storms  attended  with  considerable  wind.  But 


260 


TOLL  TELEPHONE  PRACTICE 


the  deflections  which  would  make  the  conductors  theoretically  safe 
under  such  conditions  are  not  permissible,  because  the  adjacent  spans 
would  often  swing  into  contact.  The  only  complete  remedy  is  shorter 
spans  or  stronger  wires. 

For  very  long  spans,  such  as  river  crossings,  copper  is  not  well 
suited  because  of  its  low  elastic  limit  and  moderate  strength.    Copper 

TABLE  4 

TABLE  OF  SAG  IN  HARD-DRAWN  COPPER  WIRES  FROM  THE  PRACTICE   OF   THE 
AMERICAN  TELEPHONE  AND  TELEGRAPH  COMPANY 


Deflection  in  Inches  for  Different  Temperatures  —  Fahrenheit. 

Spans  in 

Feet. 

-30 

—  10 

+10 

+30 

+60 

+80 

+IOO 

75 

I 

i-S 

i-5 

2 

2-5 

3 

4-5 

IOO 

2 

2.5 

3 

3 

4-5 

5-5 

7 

115 

2-5 

3 

3-5 

4 

5-5 

7 

9 

130 

3-5 

4 

4-5 

5-5 

7 

8-5 

ii 

150 

4-5 

5 

6 

7 

9 

"•5 

14 

2OO 

8 

9 

10.5 

12 

15-5 

19 

22.5 

has  a  tensile  strength  of  about  three  times  its  weight  per  mile,  while 
steel  has  a  corresponding  ratio  of  3.7.  The  ratios  for  silicon -bronze, 
phosphor-bronze  and  copper-clad  steel  are  about  5 ;  still  higher  ratios 
can  be  obtained  with  special  grades  of  steel.  A  wire  having  a  ratio 
of  10  has  been  used  for  spans  of  2000  to  3000  feet,  with  satisfactory 
results.  In  all  cases  conductivity  must  be  sacrificed  to  secure  in- 
creased tensile  strength. 

Poles.  —  The  poles  used  to  the  greatest  extent  in  the  United  States 
are  northern  white  cedar,  chestnut,  cypress,  northern  pine,  redwood 
and  juniper.  Of  these  the  cedar,  chestnut,  pine,  and  juniper  are  the 
most  desirable  in  the  eastern  and  central  parts  of  the  United  States 
and  cypress  in  the  south;  while  west  of  the  Rocky  mountains,  red- 
wood is  used  to  a  great  extent.  In  the  selection  of  timber,  the  locality 
in  which  it  is  to  be  used  must  always  be  considered,  both  from  the 
standpoint  of  its  life  in  the  soil  and  the  distance  it  must  be  trans- 
ported. Native  timber  is  more  economical,  in  some  cases,  by  reason 
of  the  fact  that  it  requires  little  or  no  transportation. 

Of  the  kinds  of  timber  mentioned,  white  cedar  is  undoubtedly  the 
most  extensively  used  and  is  generally  regarded  as  the  most  satis- 
factory. The  extensive  demand  for  it  has  raised  the  price  and  dimin- 


LINE  CONSTRUCTION 


261 


ished  the  supply,  however,  year  by  year.  Chestnut,  which  is  a  tough 
strong  wood  possessing  a  strength  equal  to  that  of  cedar  and  50  per 
cent  greater  elasticity,  is  displacing  cedar  to  a  considerable  extent.  One 
objection  raised  against  chestnut  is  its  crooked  growth;  this  is  a  valid 
point  for  city  lines,  but  not  in  the  case  of  ordinary  toll  lines  in  open 
country.  One  point  in  favor  of  chestnut,  which  should  not  be  over- 

TABLE  5 

AVERAGE  LIFE  OF  POLES 


Wood. 

Years. 

Chestnut  
Michigan  white  cedar  
Juniper  

8  to  15 
10  to  18 

12 

CvDress 

6  to  10 

looked,  is  its  resistance  to  fire,  or  slow  combustion,  in  which  respect 
it  is  superior  to  the  other  kinds  of  timber  mentioned.  Cedar,  on  the 
other  hand,  grows  very  dry  with  age  and  becomes  somewhat  brittle. 
This  gives  chestnut  considerable  advantage  on  or  near  steam  railroad 
right-of-way. 

The  best  poles  will  be  obtained  from  slow-growth  timber  and  should 
be  of  sound  live  wood,  squared  at  both  ends,  reasonably  straight,  and 
well  proportioned  from  butt  to  top.  They  should  be  peeled,  trimmed 
and  shaved;  the  knots  should  be  trimmed  close  and  the  final  dimen- 
sions should  be  approximately  as  given  in  Table  6.  A  pole  is  con- 
sidered commercially  or  reasonably  straight  when  a  bend  in  one 
direction  does  not  exceed  one  inch  in  every  five  feet  of  length. 

The  season  of  the  year  at  which  poles  are  cut  is  also  of  considerable 
importance.  Winter  is  generally  accepted  as  the  proper  time  for 
cutting,  since  the  conditions  at  this  season  are  the  most  favorable  for 
logging  operations;  and  at  this  season  the  tree  sap  contains  fewer 
nitrogenous  substances  from  which  fungi  obtain  their  food,  than  at 
other  seasons,  so  that  winter-cut  timber  is  the  least  liable  to  attacks 
from  this  source.  When  cut  during  the  other  seasons,  the  pole  is 
very  likely  to  be  subject  to  dry  rot,  and  although  the  pole  looks  strong 
and  substantial,  it  loses  much  of  its  strength  from  this  cause.  Fur- 
thermore, winter-cut  poles  will  season  more  gradually,  the  wood  fibers 
shrink  more  uniformly  and  checking  is  not  as  serious.  Checking  or 
splitting  is  due  to  uneven  shrinkage  as  the  process  of  seasoning  goes  on, 


262 


TOLL  TELEPHONE  PRACTICE 


and  rapid  shrinking,  except  after  the  wood  is  soaked  or  steamed,  will 
almost  invariably  result  in  serious  checking. 

The  height  of  the  poles  to  be  used  on  a  line  is  naturally  determined 
by  local  conditions  and  by  the  number  of  circuits  that  are  to  be  ulti- 
mately strung,  or  by  the  ultimate  number  of  cross-arms.  A  safe  rule 
in  this  respect  specifies  that  the  wire  shall  not  be  less  than  20  feet 

TABLE  6 

APPROXIMATE  SIZES  OF  POLES 


Length  in 
Feet. 

Circumference 
at  Top  in 
Inches. 

Circumference 
6  Feet  from 
Butt,  in  Inches. 

30 

22 

36 

35 

22 

40 

40 

22 

43 

45 

22 

47 

50 

22 

5° 

55 

22 

53 

60 

22 

56 

65 

22 

59 

70 

22 

62 

75 

22 

65 

80 

22 

69 

85 

22 

72 

90 

22 

75 

from  the  ground  at  any  point;  of  course  this  rule  is  subject  to  excep- 
tions in  such  cases  as  the  crossing  of  railroad  tracks,  where  the  height 
of  the  wires  should  be  sufficient  to  clear  trainmen  standing  on  box 
cars,  with  a  safe  margin.  In  fact  the  height  of  the  wires  at  railroad 
crossings  is  usually  regulated  by  state  laws. 

Before  leaving  the  subject  of  the  material  to  be  used  for  poles,  the 
use  of  steel  and  reinforced  concrete  will  be  mentioned  briefly.  This 
type  of  construction  is  becoming  more  important  because  the  price 
,pf  timber  is  steadily  advancing.  The  steel  poles  consist  of  three 
steel  bars,  which  are  imbedded  in  a  concrete  base  and  gradually  taper 
toward  the  top,  the  bars  being  held  in  their  relative  positions  by  steel 
bands  placed  at  regular  intervals  along  the  entire  length  of  the  pole. 
These  poles  can  be  made  of  much  greater  strength  than  the  wooden 
poles,  and  if  they  are  kept  thoroughly  painted  should  last  almost 
indefinitely.  Reinforced  concrete  poles  are  reinforced  by  steel  rods 
that  are  placed  three-quarters  of  an  inch  from  the  surface  at  the  corners 
of  the  pole,  as  shown  in  the  cross  section  in  Fig.  136.  Each  pole  is 


LINE  CONSTRUCTION 


263 


formed  on  the  ground  near  the  hole  in  which  it  is  to  be  set.  These 
poles  are  so  heavy  that  the  cost  of  transportation  for  any  material 
distance  is  generally  prohibitive.  The  framing,  roofing,  boring  and 
stepping  of  the  pole  are  all  taken  care  of  in 
the  molding.  These  poles  are  naturally  of 
very  great  strength  and  are  practically  inde- 
structible; they  should  consequently  be  of 
great  value  for  terminal  poles.  They  require  no 
attention  after  they  are  once  set,  as  the  paint- 
ing necessary  with  other  types  of  construction 
is  eliminated  and  the  concrete,  when  properly 

handled  in  construction,  improves  with  age  FlG-  X36-  —  Cr°ss  Section  of 

j  .  i  .  j  .  Concrete  Pole, 

and  is  not  subject  to  decay  or  corrosion. 

The  increased  cost  of  timber  has  focused  attention  on  the  possible 
means  of  increasing  its  life,  and  the  experiments  with  preservative 
treatments  are  worth  careful  consideration.  Such  treatment  is 
strongly  recommended  by  the  United  States  Department  of  Agri- 
culture, which,  in  conjunction  with  the  American  Telephone  and 
Telegraph  Company,  has  been  conducting  extensive  experiments  with 
various  methods.  It  has  been  estimated  by  the  government  that 
there  are  32,000,000  poles  in  use  in  the  United  States;  assuming  the 
average  life  of  a  pole  to  be  twelve  years,  it  will  require  2,670,000  poles 
annually  to  maintain  the  lines  now  in  operation.  This  enormous 
demand,  considered  in  conjunction  with  new  development,  is  a  severe 
drain  on  the  supply;  consequently,  any  method  which  will  prolong 
the  life  will  conserve  the  forests  and  reduce  the  annual  charges  on 
wooden  pole  lines. 

The  point  at  which  the  pole  enters  the  ground  and  where  it  first 
commences  to  decay  is  termed  the  wind  and  water  line.  Decay  first 
manifests  itself  here  because  the  combined  effect  of  air  and  moisture 
are  by  far  the  greatest  at  this  point;  hence  the  portion  of  the  pole 
which  is  from  two  to  eight  feet  from  the  butt  is  the  part  most  urgently 
in  need  of  treatment.  There  are  several  methods  of  treating  poles,  the 
most  important  of  which  are  known  as  the  pressure  method,  the  open- 
tank  method,  and  the  brush  method  —  each  of  which  will  be  treated 
very  briefly  in  the  order  named.1 

In  the  pressure  method  the  entire  pole  is  treated.     In  this  process 

1  For  a  more  extensive  description  of  pole  treatment,  see  the  bulletins  of  the  United 
States  Department  of  Agriculture. 


264  TOLL  TELEPHONE  PRACTICE 

the  poles  are  drawn  into  huge  horizontal  cylinders  which  are  then 
hermetically  sealed.  The  timber  is  afterward  subjected  to  live  steam 
at  a  pressure  of  about  20  pounds  per  square  inch,  for  several  hours. 
The  steam  is  then  blown  out  of  the  retorts  and  vacuum  pumps  are 
employed  to  exhaust  the  air  to  the  greatest  practical  degree.  Then 
the  preserving  fluid,  usually  creosote,  is  run  into  the  tank  and  forced 
into  the  wood  under  pressure.  After  this  the  surplus  preserving  com- 
pound is  drawn  back  into  storing  tanks  and  the  timber  allowed  to 
drip  for  a  short  time,  when  it  is  withdrawn  from  the  retorts  and  the 
process  is  completed.  The  steam  pressure  to  which  the  timber  is 
subjected  is  sometimes  allowed  to  exceed  the  twenty-pound  figure, 
but  this  is  done  at  the  risk  of  injuring  the  strength.  It  should  also 
be  remembered  that  to  secure  the  most  satisfactory  results,  the  timber 
should  be  thoroughly  seasoned  in  the  open  air  before  treatment. 

In  the  tank  method  the  wood  is  first  given  a  thorough  seasoning; 
then  the  portion  of  the  pole  which  is  to  be  treated  is  immersed  in 
an  open  tank  containing  a  hot  solution  of  the  preserving  compound. 
The  poles  are  allowed  to  remain  in  this  hot  bath  for  five  or  six  hours, 
during  which  time  the  air  and  moisture  in  the  wood  will  expand  and 
some  of  it  will  pass  out  and  appear  at  the  surface  of  the  fluid  in  small 
bubbles.  This 'part  of  the  process  is  very  similar  to  that  used  in 
boiling  out  cables  in  beeswax,  in  which  the  standard  rule  is  that  when 
bubbles  cease  to  appear  at  the  surface  of  the  liquid,  all  the  moisture 
that  can  be  expelled  has  been  driven  out.  After  the  poles  have  had 
the  required  hot  bath  they  are  transferred  as  rapidly  as  possible  to  a 
cold  solution  of  the  same  compound,  which  causes  a  contraction  of 
the  air  and  moisture  remaining  in  the  wood;  the  partial  vacuum 
thus  created  is  destroyed  by  the  entrance  of  the  preserving  fluid.  It 
will  be  noted  that  the  principles  in  these  two  processes  are  somewhat 
similar,  in  the  respect  that  the  preservative  is  forced  into  the  timber 
through  the  application  of  pressure,  artificial  pressure  being  used  in 
the  pressure  method,  while  the  atmospheric  pressure  is  utilized  in  the 
open-tank  process. 

The  third  or  brush  method  consists,  as  the  name  implies,  in  paint- 
ing the  surface  of  the  timber,  by  means  of  an  ordinary  brush,  with 
two  or  more  coats  of  hot  creosote  or  other  preservative.  This  is  by 
far  the  cheapest  method,  but  is  not  as  efficient  as  the  other  two.  In 
applying  the  preservative  great  care  should  be  taken  to  thoroughly 
fill  all  checks,  holes  and  other  defects  in  the  pole,  since  the  solution 


LINE  CONSTRUCTION  265 

will  penetrate  but  a  very  short  distance  without  pressure.  However, 
as  long  as  the  coating  of  the  preservative  around  the  surface  remains 
unbroken,  the  wood-destroying  fungi  cannot  enter.  For  this  reason 
it  is  especially  important  that  the  timber  be  thoroughly  seasoned; 
otherwise,  in  this  method,  the  drying  out  of  the  wood,  with  the 
accompanying  shrinkage,  will  cause  checking  and  thus  expose  the 
unprotected  wood  to  fungus  growths. 

This  last  process  should  be  used  only  when  the  number  of  poles  to 
be  treated  is  too  small  to  warrant  the  expense  necessary  for  the  erec- 
tion of  a  small  treating  plant.  In  all  probability  the  time  is  rapidly 
approaching  when  the  pole  dealer  will  be  required  to  treat  the  poles 
in  the  yard,  before  selling  them,  and  thus  the  small  as  well  as  the  large 
consumer  will  be  able  to  obtain  poles  that  have  received  proper  treat- 
ment. The  treatment  of  cross-arms  and  pins  is  also  advantageous. 
This  method  of  treatment  does  not  weaken  the  wood  unless  it  is  sub- 
jected to  too  high  a  temperature  or  the  process  is  too  long  continued. 
There  are  a  large  number  of  preservatives  on  the  market,  containing 
among  other  things,  in  different  percentages,  naphthaline  and  tar 
acids.  As  to  the  relative  merits  of  these  different  solutions  little  can 
be  said  at  present,  owing  to  the  lack  of  experimental  data.  Such 
data  will  be  forthcoming,  however,  when  extensive  experiments  which 
the  government  is  conducting,  in  conjunction  with  the  American 
Telephone  and  Telegraph  Company,  are  concluded.  These  experi- 
ments are  being  carried  out  on  three  hundred  cedar  and  three  hundred 
chestnut  poles,  in  the  Southern  Bell  Telephone  and  Telegraph  Com- 
pany's line  between  Wilmington  and  Pisgate,  North  Carolina,  on 
the  American  Telephone  and  Telegraph  Company's  lines  from  Dover, 
New  Jersey,  to  Thorndale,  Pennsylvania,  and  a  portion  of  the  line 
between  Warren,  Pennsylvania,  and  Buffalo,  New  York.  In  these 
lines  all  soil  conditions,  from  high  rocky  ridges  to  low  mucky  swamps, 
are  represented  and  much  valuable  information  is  hoped  for. 

The  least  that  can  be  done  in  the  way  of  preservation,  if  none  of 
the  previous  treatments  are  utilized,  is  to  heavily  coat  with  pitch, 
tar,  or  asphalt  that  portion  of  the  pole  from  the  butt  to  a  point  two  to 
four  feet  above  the  wind  and  water  line,  and  give  the  wedge-shaped 
roof  of  the  pole  the  same  treatment. 

The  probability  that  the  treatment  will  pay  is  best  illustrated  by 
the  following  quotations  from  the  government  circular  104,  on  "  Brush 
and  Tank  Pole  Treatments,"  by  Carl  G.  Crawford. 


266 


TOLL  TELEPHONE  PRACTICE 


"  Though  the  length  of  time  added  to  the  service  of  these  poles 
cannot  now  be  stated,  enough  is  known  regarding  the  value  of  the 
preservatives  as  preventatives  of  decay  to  justify  a  conclusion  as  to 
whether  the  added  life  will  repay  the  cost  of  treatment. 

"  By  the  brush  method  the  average  cost  per  pole  was  about  40 
cents,  or  29  cents  in  the  case  of  creosote,  of  which  7  cents  stands  for 
the  cost  of  oil.  By  open-tank  process  the  average  cost  per  pole  with 
creosote  (the  only  preservative  used)  was  67  cents,  of  which  22  cents 
stands  for  the  cost  of  oil. 

"  Assuming  that  the  cost  of  a  standard  3o-foot  pole  at  the  setting 
hole  is  $8,  and  that  untreated  it  will  last  twelve  years,  the  added  life 


FIG.  137.  —  Treated  Pine  Pole. 


FIG.  138.  —  Untreated  Chestnut  Pole. 


necessary  to  repay  the  cost  of  treatment  with  creosote  by  the  brush 
method  will  be  about  six  months  and  by  the  open-tank  method  about 
one  year.  A  very  conservative  estimate  of  the  added  life  by  the 
brush  method  is  thought  to  be  three  years,  which  would  mean  a  great 
saving.  In  the  tank  treatment  three  times  as  much  oil  was  absorbed 
as,  in  the  brush  treatment,  and  the  penetration  was  at  least  three 
times  as  great.  If  it  results  in  prolonging  the  life  of  the  pole  in  pro- 
portion to  the  oil  absorbed,  then  it  will  be  a  very  efficient  treatment, 
and  the  economy  of  its  use  will  be  very  great,  not  only  in  comparison 
with  no  treatment,  but  in  comparison  with  the  brush  treatment. 
The  manner  in  which  preservative  treatment  serves  to  prolong  the 
life  of  a  pole  is  strikingly  shown  by  Figs.  137  and  138." 

Pole  Line.  —  The  stability  of  the  line  depends,  in  a  great  measure, 
upon  the  proper  distribution  and  setting  of  the  poles.     A  considera- 


LINE   CONSTRUCTION  267 

tion  of  the  stresses  which  the  poles  must  ordinarily  sustain  is  par- 
ticularly important,  and  necessary  from  the  standpoint  of  laying  out 
a  route.  These  stresses  on  the  pole  can  be  readily  divided  into  four 
distinct  classes:  first,  the  compression  due  to  the  weight  of  the  cross- 
arms  and  the  wire  and  the  downward  component  of  the  wire  tension; 
second,  the  bending  moment  due  to  the  pull  on  the  wires  at  angles  or 
turns  in  the  line;  third,  the  wind  pressure  on  pole,  cross-arms  and 
wires;  fourth,  the  wind  pressure  plus  the  possible  ice  formation  or 
sleet. 

The  first,  or  compressive  stress,  can  be  entirely  neglected  in  the 
design  of  a  line,  as  the  ultimate  compressive  strength  of  timber  used 
for  poles  amounts  to  about  5500  pounds  per  square  inch,  which  obvi- 
ously gives  a  safety  factor  great  enough  to  insure  the  pole  against 
failure  even  when  exposed  to  the  most  severe  conditions  of  sleet 
formation. 

The  second  stress,  or  the  bending  moment,  which  is  encountered 
at  turns,  very  often  becomes  serious  and  reinforcement  by  guying 
is  the  remedy  generally  employed.  On  a  straight  line  these  severe 
stresses  are  not  encountered,  because  the  wire  tensions  on  one  side  of 
the  pole  are  almost  entirely  counteracted  by  those  on  the  opposite 
side.  This  is  evidently  not  the  case  at  a  turn,  and  an  approximate 
determination  of  the  stress  at  such  a  point  is,  consequently,  most 
essential.  The  ultimate  effect  of  this  stress  generally  results  in  the 
breaking  of  the  pole  near  the  surface  of  the  ground,  by  the  crushing 
of  the  wood  fibers  on  the  side  of  the  pole  subject  to  compression  and 
the  tearing  apart  of  those  on  the  opposite  side.  Fig.  139  iridicates 
the  manner  in  which  poles  usually  give  way,  which  is  a  picture  taken 
in  1909  of  a  wrecked  line  in  upper  Minnesota.  The  actual  amount 
of  pull  or  thrust  required  to  break  a  circular  pole  by  bending  has  been 
given  much  attention  in  the  past;  but  nevertheless  it  remains  rather 
an  uncertain  quantity.  It  may  be  expressed  theoretically  by 


in  which  A  is  the  area  of  the  cross  section,  D  is  the  diameter  of  the 
pole  at  the  ground  and  water  line,  S  is  the  tensile  strength  per  unit 
of  area  and  L  is  the  distance  from  the  ground  to  the  center  of  pressure. 
For  example,  assume  a  35-foot  pole  set  six  feet  in  the  ground,  with  a 
diameter  of  13  inches  at  the  ground  line;  and  assume  that  S  is  6000 


268 


TOLL  TELEPHONE  PRACTICE 


pounds  per  square  inch  and  that  the  center  of  pressure  is  24  feet  above 
the  ground,  then  the  maximum  allowable  horizontal  pull  or  load  is 

n       133  X  6000  X  13 

P  =  -^g =  4500  pounds. 

8  X  24  X  12 

The  value  of  P  just  computed  is  the  maximum  allowable  load  for  a 
fiber  stress  of  6000  pounds  per  square  inch,  but  such  a  stress  should 


FIG.  139.  —  Effect  of  Sleet  on  Pole  Line. 

never  be  permitted  in  practice;  it  is  advisable  to  use  a  factor  of  safety 
of  at  least  five,  and  in  extreme  cases  where  sleet  storms  and  high 
winds  are  to  be  expected,  ten  may  be  none  too  high.  The  value  of 
S  for  use  in  the  above  formula  varies  considerably,  but  the  6000 
pounds  per  square  inch  assumed  is  generally  a  safe  figure.  In  Table 
7  are  given  the  maximum  and  minimum  values  commonly  accepted 
for  the  tensile  strength  of  pole  timber  used  in  construction  work. 
These  values  apply  to  full-sized  poles  and  are  considerably  below  the 
values  which  can  be-  obtained  with  small  test  pieces,  of  much  more 
perfect  character. 

The  safe  maximum  value  of  P  being  ascertained,  it  is  next  in  order 
to  compare  this  figure  with  the  load  at  a  corner  or  turn  in  the  line. 


LINE  CONSTRUCTION  269 

TABLE   7 
TENSILE  STRENGTH  OF  POLE  WOODS  IN  POUNDS  PER  SQUARE  INCH 


Timber. 

Minimum. 

Maximum. 

White  cedar  
Chestnut  
Yellow  pine  

4,000 
6,000 
4,000 

8,000 
10,000 

8,000 

Cypress  

5,000 

8,000 

White  oak 

3,000 

8,000 

Referring  to  Fig.  140,  it  has  been  assumed  that  th£  total  tension  T 
in  one  direction  is  equal  to  7\  in  the  second  direction.  These  two 
forces  are  counteracted  by  two  equal  and  opposite  forces  such  as 
T'  and  TV,  or  by  R'  their  resultant  force,  determined  by  constructing 
a  parallelogram  of  forces  with  T'  and  TV.  This  resultant  force  R' 
is  equal  and  opposite  to  the  force  R,  which  is  the  resultant  of  the 


FIG.  140.  —  Diagram  of  Forces  Acting  on  a  Corner  Pole. 

weight  and  tension  of  the  wires  in  each  direction,  and  which  tends  to 
bend  or  finally  break  the  pole  in  the  direction  of  R,  as  shown  in  the 
diagram.  Therefore  the  fiber  strength  of  the  pole  must  be  great 
enough  to  resist  this  pull,  exerted  through  a  lever  arm  equal  to  the 
distance  from  the  center  of  pressure  to  the  ground  and  water  line, 
as  previously  explained.  If  the  angle  made  by  the  wires  in  the  turn 
of  the  line  be  termed  A,  then,  since  T'  =  7Y,  the  angle  made  by  the 


270  TOLL  TELEPHONE  PRACTICE 

resultant  force  R  and  either  of  the  component  forces  T'  or  T\  is 
—  -  Since  the  parallelogram  is  equilateral,  the  diagonals  intersect 
each  other  at  right  angles;  therefore 

cos-  - 

S  2       T 

or 


Hence  the  resultant  is 


R'  =  2rcos--     .    .    ......      (7) 


Assuming  again  the  use  of  No.  8  B.  &  S.  copper  wire,  stressed  to 
one-fourth  of  its  ultimate  strength,  a  specific  value  of  R'  can  be 
found.  Assuming  that  the  angle  between  the  wires  is  120°,  that  the 
pole  carries  four  cross-arms  with  40  wires,  and  using  for  Tr  the 
value  of  194  pounds  per  wire,  the  resultant  load  is 

R'  =  2  X  194  X  40  X  cos  60°  =  7760  pounds. 

This  value  is  more  than  the  breaking  load  and  guying  is  therefore,  in 
this  case,  a  necessity. 

The  third  force  to  which  a  pole  is  exposed  is  the  wind  pressure. 
The  effect  of  this  pressure  on  the  wires  has  been  determined,  and  the 
same  formula  will  suffice  for  ascertaining  its  effect  on  the  poles.  In 
the  formula 

P  =o.ospD, 

p,  as  before,  is  the  normal  pressure  in  pounds  per  square  foot  and  D 
is  the  mean  diameter  of  the  pole  in  inches.  The  value  of  P  thus 
obtained  is  the  normal  pressure  per  lineal  foot,  and  hence  the  total 
pressure  is  obtained  by  multiplying  this  quantity  by  the  number  of 
feet  of  exposed  pole.  To  illustrate,  assume  a  35-foot  pole,  set  six  feet 
in  the  ground,  with  a  1 3-inch  diameter  at  the  ground  and  a  seven-inch 
diameter  at  the  top,  or  a  mean  diameter  of  ten  inches.  Then  if  we 
assume  a  wind  pressure  of  40  pounds  per  square  foot,  the  total  lateral 
pressure  on  the  pole  becomes 

0.05  x  40  X  10  X  29  =  580  pounds. 

For  approximate  purposes  this  pressure  can  be  considered  as  acting 
at  the  middle  of  the  pole;  hence  the  corresponding  force  exerted  at 


LINE   CONSTRUCTION  271 

the  top  would  be  one-half  of  580  pounds  or  290  pounds.  To  this 
wind  pressure  of  290  pounds,  acting  on  the  pole,  must  be  added  the 
lateral  pressure  exerted  by  the  wires.  The  lateral  pressure  on  a 
No.  8  B.  &  S.  wire,  in  a  wind  having  a  pressure  of  40  pounds  per  square 
foot,  has  been  previously  computed  as  0.256  pound  per  linear  foot. 
Then  assuming  four  cross-arms  per  pole,  which  will  carry  forty  wires, 
the  poles  being  spaced  at  130  feet,  the  total  wind  pressure  on  the 
wires  is 

0.256  X  40  X  130  =  1330  pounds. 

Added  to  the  290  pounds  of  wind  pressure  exerted  on  the  pole  itself, 
at  the  top,  this  gives  a  total  load  of  1620  pounds.  This  is  well  below 
the  ultimate  strength  of  the  pole,  but  the  assumption  of  a  moderate 
load  of  sleet,  in  addition,  will  carry  the  stresses  far  beyond  the  safe 
limit.  Thus  a  wind  pressure  of  20  pounds  per  square  foot,  with  an 
ice  coating  on  No.  8  B.  &  S.  wires  of  three-eighths  of  an  inch,  gives, 
from  previous  calculations,  a  load  of  0.923  pound  per  lineal  foot. 
This  gives  in  turn,  for  40  wires  with  a  span  of  130  feet,  a  wind  load  of 

0.923  X  40  X  130  =  4800  pounds. 

Adding  to  this  the  wind  load  on  the  pole  alone  gives  a  total  of  5090 
pounds,  or  more  than  the  breaking  load,  assuming  that  the  wires 
themselves  would  sustain  their  individual  loads.  The  effects  that  a 
storm  will  have  on  a  line  that  is  faulty  in  design  and  one  that  is  well 
reinforced  is  clearly  shown  in  Figs.  141  and  142.  These  lines  paral- 
leled one  another  and  the  effect  of  the  storm  was  to  completely  wreck 
the  one,  while  the  other  remained  uninjured.  This  shows  the  ad- 
visability of  utilizing  a  large  factor  of  safety  in  the  design  of  the  line. 

In  some  parts  of  the  country  where  severe  sleet  storms  and  high 
winds  are  of  frequent  occurrence,  a  special  type  of  construction  has 
been  used.  This  consists  of  setting  two  poles  where  it  is  the  usual 
I  practice  to  set  one.  These  two  poles  are  set  about  six  feet  apart  at 

the  bottom  and  brought  together  and  firmly  bolted  at  the  top,  and 
the  cross-arms  fastened  to  both  poles.  This  undoubtedly  greatly 
strengthens  the  line,  but  like  results  can  be  obtained  by  decreasing  the 
span  and  thus  the  strain  on  the  wires.  However,  the  local  conditions 
in  each  case  must  determine  which  is  the  best  practice. 

A  thorough  grasp  of  the  principles  involved  in  the  design  of  a  pole 
line  is  very  essential  in  laying  out  a  route.  The  first  step  in  actual 
location,  which  should  precede  the  distribution  of  material,  is  staking 


272 


TOLL  TELEPHONE  PRACTICE 


out  the  route.  Assuming  that  the  poles  are  to  be  spaced  130  feet 
apart,  the  staking  is  commenced  by  driving  a  stake  into  the  ground 
where  the  first  pole  is  to  be  located  and  at  the  proper  distance  from 
the  center  of  the  road  or  the  fence.  The  succeeding  stakes  are  located 
by  measuring  off  130- foot  lengths  on  the  straight  sections,  while  at 


FIG.  141.  —  Effect  of  Sleet  on  a  Poorly  Constructed  Pole  Line. 

curves  or  corners  the  poles  must  be  placed  as  near  together  as  may 
be  necessary  to  carry  the  ultimate  number  of  circuits  for  which  the 
route  is  designed. 

It  is  customary,  in  order  to  reduce  the  stress  on  the  pole,  to  limit 
the  spacing  of  the  poles  on  either  side  of  a  corner,  at  right-angled 
corners  and  road  crossings,  to  75  feet.  Also  the  last  section  at  a  line 
terminal  and  the  sections  on  either  side  of  a  long  span,  say  200  feet 
or  more,  should  not  exceed  75  feet.  In  placing  the  stakes  it  is  ad- 
visable to  sight  from  stake  to  stake  so  as  to  insure  a  straight  line. 


LINE  CONSTRUCTION 


273 


In  crossing  rivers  and  surmounting  other  natural  obstacles  great 
care  should  be  exercised  in  locating  the  poles,  to  secure  a  setting  in 
firm  soil;  it  is  well,  for  example,  not  to  approach  too  close  to  the  edge 
of  a  river  or  stream,  even  at  the  expense  of  lengthening  the  crossing. 
If,  in  so  doing,  the  length  of  the  span  greatly  exceeds  the  standard 


FIG.  142.  —  Effect  of  Sleet  on  a  Properly  Braced  Pole  Line. 

of  130  feet,  the  poles  at  the  banks  must  be  extra  large  and  well  guyed 
to  stand  the  additional  stresses  which  they  will  receive. 

It  is  very  desirable  to  lay  out  a  map  of  the  pole  route,  showing  the 
proposed  location  of  stakes  and  the  distances  between  them,  before 
the  final  route  is  selected.  In  building  lines  along  the  right  of  way  of 
a  railroad,  it  is  best  to  keep  the  poles  at  a  distance  of  12  feet  from 
the  edge  of  the  nearest  rail,  unless  the  lowest  cross-arm  is  placed  more 
than  22  feet  above  the  top  of  the  rail,  in  which  case  the  pole  may  be 
set  not  less  than  seven  feet  from  the  rail. 


274  TOLL  TELEPHONE  PRACTICE 

All  poles  on  which  turns  are  made  are  exposed  to  extra  stresses  and 
should  be  well  guyed.  It  is  therefore  essential  to  show  on  the  map, 
previously  referred  to,  the  location  of  the  guy  stubs  and  anchors,  so 
that  they  may  be  staked  off  when  the  pole  route  is  being  laid  out. 
Another  item  that  should  be  considered  in  planning  the  pole  route  is 
the  matter  of  grading  the  pole  tops.  This  is  of  little  if  any  impor- 
tance in  a  level  country,  but  in  a  hilly  country  it  should  receive  ample 
consideration,  as  will  be  evident  by  a  glance  at  Figs.  143  and  144. 


FIG.  143.  —  Ungraded  Pole  Line. 

It  is  apparent  that  the  length  of  the  poles  should  be  proportioned  to 
the  contour  of  the  country,  thus  avoiding  any  abrupt  changes  in  the 
level  of  the  wires;  for  if  the  poles  are  all  of  the  same  length,  those  on 
either  side  of  the  one  at  the  bottom  of  the  valley  will  be  subjected  to 
extra  stresses,  while  the  pole  in  the  valley  would  have  an  upward  pull, 
which  is  very  likely  to  pull  off  insulators  and  in  extreme  cases  lift 
the  pole  out  of  the  ground.  The  rise  or  fall  in  the  level  should  not 
exceed  five  feet  between  poles.  Fig.  144  shows  how  this  difficulty  is 


FIG.  144.  —  Graded  Pole  Line. 

very  easily  overcome  by  the  use  of  long  and  short  poles.  The  re- 
quired lengths  of  the  poles  can  be  readily  estimated  by  an  experienced 
man,  if  the  level  of  the  country  is  not  subject  to  unusual  variations; 
but  in  very  hilly  country  it  may  be  profitable  to  make  a  preliminary 
survey  of  the  route,  from  which  a  profile  map  may  be  prepared  to  aid 


LINE   CONSTRUCTION  275 

in  selecting  pole  lengths.  When  these  preliminaries  have  been  com- 
pleted the  distribution  of  material  may  be  commenced. 

In  this  connection  it  should  be  remembered  that  the  pole  ought  to 
be  placed  with  the  butt  end  closest  to  the  stake,  and  that  if  the  country 
is  hilly  the  small  end  of  the  pole  should  be  located  at  the  highest  point 
of  the  grade.  By  observing  these  suggestions  the  work  of  the  pole- 
raising  gang  will  be  greatly  facilitated.  It  hardly  seems  necessary 
to  add  that  the  stoutest  poles  should  be  placed  at  the  corners  and 
points  where  exceptional  stresses  are  likely  to  be  encountered.  The 
poles  of  best  appearance  should  be  used  in  towns  and  cities.  The 
method  of  distribution  is  governed,  to  a  very  large  extent,  by  local 
conditions.  However,  when  the  route  parallels  a  railroad  it  is  often 
feasible  to  drop  the  poles  at  their  proper  places  from  the  car  on  which 
they  have  been  transported. 

After  the  poles  have  been  distributed,  and  before  they  are  set,  they 
should  be  properly  framed  and  gained.  Poles  are  usually  received 
from  the  yards  with  their  butt  ends  nearly  flat;  if  this  is  not  the 
case,  they  should  be  so  cut  before  setting.  The  pole  should  be  cut 
for  the  ultimate  number  of  cross-arm  gains,  and  the  small  end  of  the 
pole  roofed  as  shown  in  Fig.  145.  These  gains  should  measure  4  by 
4j  inches  and  one-half  inch  deep,  when  braces  are  used,  as  shown  in 
the  figure.  If  no  cross-arm  braces  are  used  it  is  advisable  to  make 
the  gain  at  least  three-quarters  of  an  inch  deep.  The  center  of  the 
upper  gain  should  be  ten  inches  from  the  apex  of  the  pole.  When  the 
gains  have  been  cut,  and  before  the  cross-arms  are  placed  in  position, 
a  f-inch  hole  should  be  bored  through  the  pole  at  the  center  of  each 
gain,  but  no  holes  should  be  bored  in  the  spare  gains.  The  remaining 
gains  should  be  bored  when  used.  The  roof  and  the  gains  should  be 
painted  with  two  or  three  coats  of  the  best  white  lead,  or  carbolineum 
avenarius.  This  prevents  the  moisture  from  entering  the  wood  and 
helps  materially  to  prolong  the  life  of  the  pole. 

The  cross-arms  should  be  made  of  sound,  thoroughly  seasoned, 
straight-grained  wood  which  is  free  from  heart  and  sapwood  and  free 
from  all  such  knots  as  would  tend  to  weaken  them.  All  cross-arms, 
when  not  creosoted,  should  be  thoroughly  painted  with  two  coats  of 
standard  paint.  The  wood  that  is  used  for  cross-arms  is  regulated, 
like  the  timber  for  poles,  by  the  locality  where  it  is  to  be  used.  The 
timbers  most  preferred  are  Norway  pine,  long-leaf  yellow  pine,  and 
red  and  black  cypress.  The  top  of  the  cross-arm  should  be  rounded, 


276 


TOLL  TELEPHONE  PRACTICE 


FIG.  145.  —  Pole  With  Gains  Cut  for  Cross-Anns. 


LINE   CONSTRUCTION 


277 


so  that  the  rain  will  readily  run  off.  The  dimensions  naturally  depend 
upon  the  load  it  will  be  required  to  carry.  Two  regular  sizes  are  on 
the  market,  the  standard  arm  and  the  telephone  arm;  for  toll  work  the 
former  should  be  used  exclusively.  Standard  cross-arms  measure  3^ 


-/o'-q 


•  zi' 


-*   ;i 


r* 


t —  /g* — »L —  ig.* — — —  /g"   ilf    /a* — J*_  e*-. 
)  O  cb<V  o  ©I 


e'JL-  iz'  .1.     /«•-! — iz'-JL-  /g'— *U: 
]©          (hi-         6         *<b          <b 


by 


FIG.  146.  —  Standard  Ten-pin  Cross-Arm. 

inches  and  vary  in  length  from  three  to  ten  feet,  depending  upon 


the  number  of  pins.  The  dimensions  of  a  standard  ten-pin  arm  are 
shown  in  Fig.  146;  the  number  of  pins,  the  distances  between  them, 
and  the  approximate  weights,  for  various  lengths,  are  given  in  Table  8. 

TABLE  8 

DIMENSIONS  OF  STANDARD  CROSS-ARMS 


Length  in 
Feet. 

Number 
of  Pins. 

Spacing  of  Pins  in  Inches. 

Approximate 
Weight  in 
Pounds. 

Ends. 

Center. 

Sides. 

3 

2 

4 

28 

9 

4 

4 

4 

16 

12 

12 

5 

4 

4 

18 

17 

IS 

6 

4 

4 

22 

21 

18 

6 

6 

4 

16 

12 

18 

8 

6 

4 

18 

17* 

24 

8 

8 

4 

16 

12 

24 

10 

8 

4 

i7i 

15! 

30 

10 

10 

4 

16 

12 

30 

The  cross-arms  are  best  secured  in  position  by  a  f -inch  iron  machine 
bolt,  which  passes  through  the  pole.  The  bolt  should  be  long  enough 
to  go  through  the  cross-arm  and  the  pole  without  cutting  away  the 
back  of  the  pole.  It  should  be  driven  through  from  the  back  of  the 
pole,  a  large  square  washer  being  placed  under  the  head.  A  similar 
washer  should  be  placed  on  the  cross-arm  under  the  nut.  This  con- 
struction is  much  superior  to  the  old  practice  of  fastening  the  cross- 
arm  with  two  lag  screws;  it  also  facilitates  renewals,  since  the  lag 
screws  tend  to  loosen  as  the  pole  ages. 


278 


TOLL  TELEPHONE  PRACTICE 


The  cross-arm  should  be  further  secured  by  means  of  two  iron  or 
mild  steel  braces,  of  the  dimensions  shown  in  Fig.  147.     They  are 


30* 


FIG.  147.  —  Standard  Cross-arm  Brace. 

usually  20  to  30  inches  long  and  ij  inches  wide,  by  one  quarter  of  an 
inch  thick.     Each  pair  of  braces  is  fastened  to  the  pole  by  means  of  a 


FIG.  148.  —  Standard  Method  of  Bracing. 

single  lag  screw,  about  five  inches  long;  the  opposite  ends  are  attached 
to  the  cross-arm  above  by  means  of  f-inch  carriage  bolts.     There 


LINE  CONSTRUCTION 


279 


should  be  washers  under  each  end  of  the  bolt  and  the  nut  should  be 
on  the  brace  side  of  the  arm.  The  standard  method  of  bracing  is 
shown  in  Fig.  148.  The  use  of  braces  keeps  the  cross-arms  in  align- 
ment and  allows  the  gains  to  be  shallow,  thus  adding  strength  to  the 
pole.  The  braces  should  be  attached  to  the  front  of  the  arm  and 
the  bolts  should  be  slightly  above  the  center. 

At  all  points  where  the  load  will  be  exceptional,  such  as  office  ter- 
minal poles,  railroad  and  river  crossings,  or  exceedingly  long  spans, 
the  poles  should  be  equipped  with  double  cross-arms.  In  these  cases 
the  double  arms  should  be  provided  with  blocks  of  wood  between 
them,  held  in  place  by  carriage  bolts  which  pass  through  the  blocks 
and  both  arms. 

The  cross-arms  should  always  be  drilled  for  the  ultimate  number  of 
pins.  There  are  three  standard  sizes  of  pins,  as  shown  in  Fig.  149; 


FIG.  149.  —  Standard  Sizes  of  Pins. 

A  is  the  transposition  pin,  B  the  ordinary  line  pin  and  C  the  terminal 
pin.  These  pins  are  commonly  made  of  locust,  chestnut  or  oak. 
The  locust  pin  is  much  stronger  than  oak  and  should  be  employed 
for  toll-line  construction,  although  the  original  cost  is  greater.  The 
specifications  usually  require  that  the  pin  shall  be  made  of  the  best 
quality  of  split  locust,  sound,  straight-grained  and  free  from  knots 
and  sap  wood. 


280 


TOLL  TELEPHONE  PRACTICE 


The  shank  of  the  pin  is  usually  tapered  toward  the  end,  where  it 
is  about  one  thirty-secondth  of  an  inch  smaller  than  the  hole  in  the 
cross-arm.  Thus  it  is  readily  driven  into  the  arm  and  held  securely. 
It  should  also  be  fastened  in  place  by  means  of  a  six-penny  nail,  driven 
through  the  arm.  The  upper  part  of  the  pin  is  tapered  slightly  and 
provided  with  a  coarse  thread  to  receive  the  insulator.  Steel  pins  can 
also  be  obtained  and  are  used  to  some  extent  on  telegraph  lines;  the 
top  of  the  pin  is  provided  with  a  wooden  thimble  to  receive  the  insu- 
lator. Such  pins  are  rarely  used  in  telephone  construction  and  are 
not  recommended. 

It  is  standard  practice  to  fit  every  tenth  pole  and  each  office  or 
terminal  pole  with  lightning  rods,  which  consist  of  No.  6  or  No.  8 
B.  W.  G.,  heavy  galvanized  iron  wire.  About  six  feet  of  this  wire 
should  be  formed  into  a  flat  coil  and  placed  in  the  hole  under  the  butt 
of  the  pole;  it  should  be  stapled  up  the  pole  on  the  side  opposite  the 
cross-arm  and  project  several  inches  above  the  top. 

TABLE  9 

DEPTH  OF  POLE  SETTING 


Length  of  Pole 
in  Feet. 

Depth  in 
Ground  in 
Feet. 

Remarks. 

3° 

5* 

Straight  line. 

30 

6 

Corner. 

35 

6 

40 

6 

45 

6* 

50 

7 

55 

7l 

60 

8 

65 

8* 

70 

9 

75 

ti 

80 

10 

85 

I0| 

90 

II 

In  setting  the  poles  each  hole  should  be  dug  with  the  marking  stake 
as  a  center  and  made  large  enough  to  admit  the  pole  freely,  which 
means  that  the  hole  should  be  from  four  to  six  inches  larger  than  the 
base  of  the  pole.  The  hole  should  be  full  size  at  the  bottom  so  as  to 
permit  the  proper  use  of  tamping  bars.  The  depth  to  which  poles 
should  be  set  is  naturally  governed  by  their  height  and  the  nature  of 
the  soil.  For  average  conditions  the  depths  are  given  in  Table  9.  In 


LINE  CONSTRUCTION 


281 


order  to  prevent  caving,  the  excavations  should  stand  open  but  a 
short  time.  This  may  be  accomplished  by  setting  the  entire  gang 
digging  holes  in  the  forenoon  and  setting  the  poles  in  the  afternoon 
or  dividing  the  gang  in  two  parts.  As  to  the  number  of  poles  that 
should  be  set  per  day  little  can  be  said,  as  this  is  governed  entirely  by 
the  number  of  men  and  the  local  conditions  and  can  be  readily  deter- 
mined by  the  foreman  after  the  gang  has  been  working  several  days. 
It  may  be  of  interest  to  note,  however,  that  it  takes  about  six  men  to 
raise  a  3 5 -foot  pole,  and  this  number  gradually  increases  with  the 
weight  and  length  of  the  pole;  in  extreme  cases  from  15  to  20  men 
are  required.  These  figures  are  based  upon  the  assumption  that  the 


FIG.  150. 
Pike  Pole. 


FIG.  151. 
Dead  Man. 


FIG.  152. 
Pole  Support. 


FIG.  153 

Raising  Fork. 


poles  are  raised  by  the  ordinary  method  of  pike  poles  (Fig.  150),  dead- 
man  (Fig.  151),  pole  support  (Fig.  152),  and  raising  fork  (Fig.  153), 
which  is  the  usual  practice  on  toll  lines,  as  a  derrick  wagon  can  only 
be  used  under  favorable  conditions. 
After  the  pole  has  been  brought  to  a  vertical  position  it  should  be 


282 


TOLL  TELEPHONE  PRACTICE 


turned  by  means  of  a  cant  hook  (Fig.  154),  until  the  cross-arm  is  at 
right  angles  to  the  direction  of  the  line.  The  proper  facing  of  cross- 
arms  on  a  tangent  is  shown  at  A  in  Fig.  155,  which  pre- 
vents  them  from  stripping  from  the  poles  under  excessive 
longitudinal  stresses.  Further  rules  regarding  the  facing 
of  cross-arms  are  as  follows:  On  long  sections  the  cross- 
arms  shall  be  placed  on  the  side  of  the  pole  away  from 
the  span,  and  at  the  terminals  the  cross-arms  on  the  last 
two  poles  shall  be  placed  on  the  side  of  the  pole  facing 
the  terminal.  On  all  curves  the  cross-arms  shall  be  placed 
on  the  side  of  the  pole  facing  the  middle  of  the  curve, 
while  at  road  crossings  they  shall  be  placed  on  the  side  of 
the  pole  that  faces  the  road,  as  at  B  in  Fig.  155. 

When  the  raised  pole  has  been  turned  to  the  proper  po- 
FIG.  154.  —  sition  it  should  be  temporarily  braced,  which  may  be  ac- 
Cant  Hook.  complished  by  means  of  four  pike  poies>  The  back  filling 

and  tamping  should  be  done  carefully  and  thoroughly,  so  as  to  give 
the  pole  a  firm  setting.  A  standard  tamping  bar  is  shown  in  Fig.  156. 
The  soil  should  then  be  firmly  banked  around  the  pole  about  one 


FACING    OF   CROSS    ARMS    ON    STRAIGHT  LINE 


FACING   OF  CROSS  ARMS 
AT    ROAD    CROSSING 


FIG.  155.  —  Facing  of  Cross-Arms  on  Pole  Line. 

foot  above  the  surface  of  the  ground.  If  the  work  is  done  properly 
this  will  generally  dispose  of  all  excavated  material.  The  foreman 
should  so  divide  the  labor  that  every  man  will  be  at  work,  practically 
without  interruption  or  delay,  and  to  this  end  he  should  remain  with 
the  gang  at  all  times.  If  it  is  occasionally  necessary  for  him  to  be 
absent,  a  competent  assistant  should  be  left  in  charge. 


LINE  CONSTRUCTION 


283 


284  TOLL  TELEPHONE  PRACTICE 

At  all  points  where  poles  will  be  exposed  to  an  exceptionally  heavy 
load  they  should  be  given  an  angle  of  inclination  in  a  direction  oppo- 
site from  that  of  the  load.  This  is  termed  raking,  and 
the  rake  should  vary  from  12  to  18  inches,  depending 
upon  the  stresses.  In  some  cases  the  next  three  or  four 
poles  on  either  side  are  raked  also,  each  in  a  gradually 
decreasing  proportion  until  the  vertical  position  is  again 
obtained. 

ill  Quite  frequently  it  becomes  necessary  to  set  poles  in 

soft  ground  such  as  marshes  and  swamps,  and  in  these 
cases  artificial  foundations  must  be  resorted  to.  Of 
course  the  type  of  foundation  is  regulated,  to  a  large 
extent,  by  the  local  conditions.  Several  methods  are 
shown  in  Fig.  157.  It  will  be  observed  that  in  all  these 
schemes,  except  the  one  in  which  concrete  is  employed, 
a  flat  wooden  structure  is  built  at  the  base  of  the  pole 
so  as  to  provide  a  large  bearing  surface  and  secure 
bracing.  On  curves,  in  soft  ground,  a  method  of  brac- 
ing such  as  that  shown  in  Fig.  158  is  often  used  to 
great  advantage.  The  logs  attached  to  the  pole  greatly 
FIG.  156.  —  increase  the  bearing  surface  and  add  to  the  general 

Tamping  Bar. 

stability. 

Guying.  —  The  extra  loads  at  corners,  curves,  terminal  poles  and 
long  spans  make  it  necessary  to  reinforce  the  line  by  guying.  Braces 
are  often  used  in  place  of  guys  and  are  frequently  superior.  The 
method  of  reinforcement  depends  to  a  large  extent  upon  local  con- 
ditions. Some  of  the  standard  methods  are  shown  in  what  follows. 

One  form  of  guy  is  shown  in  Fig.  159,  and  is  known  as  the  Y  guy. 
With  this  form  of  guy  the  stress  is  about  evenly  divided  between  the 
two  branches  of  the  Y.  A  straight  guy  attached  to  the  pole  near 
the  center  of  the  load  is  easier  to  install  and  about  as  effective;  it 
is-  the  type  generally  employed.  The  guy  should  never  be  attached 
to  the  top  of  the  pole  or  below  the  arms. 

Another  method  of  reinforcement  is  known  as  head  guying  and  is 
shown  in  Fig.  160.  In  this  method  the  top  of  the  pole  is  guyed  to  the 
bottom  of  the  next,  at  a  point  10  to  12  feet  above  the  ground. 
For  general  reinforcement  head  guys  should  be  run  in  each  direction. 
The  bracing  of  the  line  in  both  directions  can  also  be  accomplished 
between  one  pair  of  poles  by  what  is  known  as  double  head  guying, 


LINE  CONSTRUCTION 


285 


FIG.  158.  —  Method  of  Bracing  Pole  in  Marshy  Soil. 


FIG.  159.  —  Side  Guying. 


286 


TOLL  TELEPHONE  PRACTICE 


FIG.  1 60.  —  Head  Guying. 


FIG.  161.  —  Double  Head  Guying. 


FIG.  162.  —  Head  Guying  on  Grades. 


LINE  CONSTRUCTION 


287 


as  shown  in  Fig.  161.  In  general  it  is  superior  practice,  however,  to 
attach  the  guys  to  anchors  in'stead  of  the  butts  of  poles.  A  method 
of  head  guying  on  heavy  grades,  to  carry  the  weight  of  the  line,  is 
shown  in  Fig.  162.  This  method  does  much  to  relieve  the  component 
of  load  on  the  poles  caused  by  the  downward  tension  of  the  wire, 
which  tends  to  pull  the  top  of  the  pole  downhill. 


FIG.  163.  —  Guy  Stub  and  Anchor. 

The  methods  of  anchoring  guy  wires  which  take  up  the  side  strains 
naturally  vary  according  to  conditions.  The  usual  method  when  direct 
anchoring  is  not  practical  is  to  use  a  guy  stub.  The  poles  used  for  guy 
stubs  should  meet  the  general  specifications  required  for  standard  poles. 

There  are  several  methods  of  installing  a  guy  stub.  The  one  shown 
in  Fig.  159  is  used  to  some  extent,  but  the  one  shown  in  Fig.  163, 
utilizing  a  guy  stub  and  anchor,  is  more  generally  employed.  The 
stub  shown  in  the  latter  figure  should  be  roofed,  after  the  manner  of 


288 


TOLL  TELEPHONE  PRACTICE 


poles,  and  all  stubs  when  not  creosoted  should  be  treated  in  a  manner 
similar  to  that  specified  for  poles.  When  it  is  impossible  to  locate 
an  anchor  for  a  guy  stub  as  shown  in  Fig.  163,  the  stub  should  be 
braced  as  shown  in  Fig.  164.  When  possible  all  guy  stubs  should  be 
set  in  the  ground  to  a  depth  of  six  feet  and  should  be  inclined  or  raked 
away  from  the  pole  as  shown  in  Fig.  164.  Modern  practice  has 
revolutionized  the  methods  of  guying;  it  was  customary  formerly  to 


FIG.  164.  —  Method  of  Bracing  Guy  Stub. 

use  a  guy  stub  whenever  conditions  were  favorable,  but  its  use  is  now 
confined  to  such  places  as  road  crossings,  where  an  anchor  guy  is  not 
permissible. 

The  old  standard  method  of  anchoring  a  guy  is  by  means  of  a  guy 
rod  and  anchor  log  as  shown  in  Fig.  158.  The  standard  guy  rod 
should  be  made  of  good  wrought  iron  and  of  the  general  dimensions 
shown  in  Fig.  165.  This  rod  is  passed  through  the  center  of  the 
anchor  log  and  is  fastened  by  means  of  a  square  washer  and  nut. 
The  excavation  for  a  log,  ten  inches  in  diameter  and  4^  feet  in  length, 
should  be  six  feet.  If  it  is  impossible  to  attain  this  depth,  on  account 


LINE  CONSTRUCTION 


289 


of  the  nature  of  the  soil,  an  excavation  of  only  four  feet  will  suffice,  but 
in  this  case  the  dimensions  of  the  log  should  be  increased.  In  Table 
10  are  given  the  general  dimensions  of  anchor  logs  and  the  depths 


FIG.  165.  —  Standard  Guy  Rod. 


to  which  they  should  be  buried.  The  log  should  be  firmly  anchored 
by  a  covering  of  planks,  logs,  rocks  or  any  other  available  material 
that  will  increase  the  bearing  surface. 

Another  type  of  guy  anchor  that  seems  to  have  met  with  con- 
siderable satisfaction  is  the  one  manufactured  by  the  Miller  Anchor 

TABLE   10 
DIMENSIONS  OF  ANCHOR  LOGS 


Depth  of 
Excavation. 

Length  of 
Log. 

Diameter  of 
Log. 

5  feet 

5  feet 

16  inches 

5 

8     " 

10      " 

4    ' 

5     " 

23      " 

4     " 

8     "    - 

14       " 

4     " 

10     " 

12 

Company.  Fig.  166  shows  the  anchor  and  the  method  of  installation, 
from  which*  it  will  be  noted  that  the  method  of  setting  is  exceedingly 
simple.  The  anchor  is  first  inserted  in  a  hole  which  has  been  bored 
at  an  angle  that  the  guy  will  ultimately  assume,  and  then  the  upper 
end  of  the  spoon  is  tilted  downward  with  an  ordinary  bar.  This 
causes  the  lip  to  engage  with  the  soil  or  gravel  and  when  the  rod  is 
pulled  upward  the  spoon  will  assume  a  position  at  right  angles.  The 
hole  is  then  refilled  and  well  tamped.  The  spoons  are  made  of  cast 
iron,  while  the  rods  are  wrought  iron.  The  anchor  has  a  great  hold- 
ing power  due  to  the  fact  that  when  it  opens  out  a  firm  grip  is  secured 
on  the  undisturbed  earth  on  either  side  of  the  hole.  It  should  be  set 
from  five  to  ten  feet  deep,  depending  upon  the  load  which  it  is  to 
carry.  The  manufacturer  advises  that  the  load  should  be  governed  by 


290 


TOLL  TELEPHONE  PRACTICE 


the  size  of  the  wrought-iron  rod,  which  will  break  before  the  spoon 
will  pull  out.     The  tensile  strength  of  these  rods  is  given  in  Table  n. 


FIG.  1 66.  —  Miller  Anchor. 

Still  another  type  of  guy  anchor  is  the  Matthews,  formerly  known 
as  thje  Stombaugh,  which  consists  of  a  steel  rod  and  eye  to  which  is 
rigidly  attached  a  piece  of  cast  iron,  helical  in  shape;  the  lower  edge 

TABLE  II 

STRENGTH  OF  WROUGHT-IRON  ANCHOR  RODS 


Diameter  in 
Inches. 

Tensile 
Strength  in 
Pounds. 

% 

9,800 

% 

I5.340 

% 

22,090 

I 

39,270 

3 

49,700 
61,360 

of  the  helical  piece  is  sharp  and  will  screw  into  the  ground  without 
disturbing  it.  When  thus  embedded  in  solid  undisturbed  earth  it  has 
a  very  great  holding  power.  Owing  to  the  simplicity  with  which  it 


LINE  CONSTRUCTION 


291 


can  be  installed,  it  is  frequently  used  where  soil  conditions  are  favor- 
able. These  anchors  are  shown  in  Fig.  167,  and  in  Table  12  fe  given 
the  holding  power  of  the  different-sized  anchors  when  screwed  five  feet 
into  clay  soil,  as  calculated  by  Professor  R.  C.  Carpenter. 


KiOO 


1000 


/ 


7O4.  R             605  R          SO 

&.-;  t   9    C 

2  R 

| 

t 

K 
kl 

hi 
Ik 

<0 

*4^ 
P^ 

SN 

' 

^4 

^> 

V"^       *V          ^r^^    *V^ 
eiN»         7  IN.        /9eiN>       5IM* 

r~v*s/^7 

«'N-\on  '°o 

lEIN.  «O«N,Jo) 

^^^r 

^oo    vSM  em. 


FIG.  167.  —  Matthews  Anchor. 

Fig.  1 68  illustrates  the  theory  from  which  the  holding  power  of 
this  type  of  anchor  is  deduced.  The  resistance  offered  by  the  earth 
is  represented  by  the  weight  of  an  inverted  cone,  the  angle  of  whose 
apex  is  90°.  The  holding  power  will  be  readily  seen  to  be  very  great 
when  the  weight  of  the  earth  in  the  cone  and  the  cohesive  qualities 
of  the  undisturbed  ground  are  taken  into  consideration.  For  instance, 
consider  a  1 2-inch  anchor  bored  five  feet  into  the  ground ;  the  resistance 


TOLL  TELEPHONE  PRACTICE 


TABLE  12 

SIZE  AND  HOLDING  POWER  OP  MATTHEWS  GUY  ANCHORS 


Diameter 
in  Inches. 

Size  and  Shape 
of  Rods. 

Weight  in 
Pounds. 

Holding 
Power  in 
Pounds. 

Remarks. 

5 

None. 

2i 

12,500 

)  Used  where  no  objection  exists 

6 

None. 

4i 

15,000 

|      to  burying  strand. 

6 

7 

\  in.  round, 
f  in.  round, 
f  in.  round. 

10 

15 

12,500 
15,000 
17.500 

f  These   sizes   require   a    wrench 
C     for  installing. 

8 

if  in.  square. 

38 

2O,OOO 

)  These  sizes  are  installed  by  plac- 

10 

ij  in.  square. 

50 

25,000 

ing  a  digging  bar  through  the 

12 

i£  in.  square. 

80 

30,000 

)     eye. 

to  an  upward  pull  will  be  represented  by  a  cone  which  is  five  feet  from 
apex  to  base  (or  surface  of  the  ground)  and  approximately  ten  feet 
across  the  base,  assuming  a  perpendicular  axis.  (The  anchor  should 
always  be  installed,  however,  at  the  same  angle  as  the  guy  wire.) 
This  cone  contains  a  little  over  170  cubic  feet  of  earth,  which  weighs 


FIG.  168.  —  Theory  of  Holding  Power  of  Matthews  Guy  Anchor. 

in  the  neighborhood  of  20,000  pounds.  The  balance  of  the  resistance 
is  due  to  the  cohesive  properties  of  the  undisturbed  ground.  This 
also  applies  to  the  smaller  anchors,  in  a  less  degree.  The  holding 
power  of  one  of  these  anchors,  according  to  Professor  Carpenter,  can 
be  computed  by  the  formula, 

R  =  iooDH2, (8) 


LINE  CONSTRUCTION  293 

in  which  R  is  the  pull  on  the  guy  wire  in  pounds,  H  is  the  depth  in 
feet  to  which  the  anchor  is  placed  and  D  the  diameter  of  the  helix  in 
inches.  Thus  if  the  anchor  having  a  helix  12  inches  in  diameter  is 
screwed  to  a  depth  of  five  feet,  the  total  holding  power  would  be 

R  =  100  X  12  X  25  =  30,000  pounds. 

The  following  is  a  quotation  from  the  instructions  issued  by  a  large 
telephone  company  showing  how  and  where  this  anchor  is  to  be  used. 

"  Where  the  soil  conditions  are  favorable  (sand,  loamjor  clay),  the 
Matthews'  Anchor  may  be  used  as  a  substitute  for  the  standard  log 
or  plank  anchor  as  enumerated  below. 

"  This  type  of  anchor  in  six-inch,  eight-inch,  and  ten-inch  sizes  is 
approved  for  use  as  follows: 

"(a)  Toll  lines  of  12  to  20- wire  capacity,  six  inches  or  eight  inches, 
according  to  strain. 

u(b)  Toll  lines  of  40- wire  capacity,  except  for  heavy  corners  or  route 
ends,  eight  inches  only.  Log  or  plank  anchors  must  be  used  for  points 
of  heavy  strains  except  as  above. 

"(c)  Farmers'  lines,  six  inches  under  all  conditions. 

"(d)  Exchange  aerial  open- wire  leads  not  exceeding  40  wires,  eight 
inches  or  ten  inches,  according  to  strain  and  soil. 

11 (e)  Exchange  aerial  cable  not  exceeding  ico-pair,  No.  22  gauge, 
eight  or  ten  inches  on  all  main  leads  and  on  branches  larger  than 
2 5 -pair,  six  inches  on  legs  not  exceeding  25  pairs. 

UA11  anchors  must  beset  at  least  five  feet  below  the  surface  of  the 
earth." 

There  are  several  other  types  of  anchors  on  the  market  which  have 
given  more  or  less  satisfaction,  but  the  limits  of  space  prevent  their 
description  in  detail. 

Guys  are  sometimes  attached  to  suitable  trees,  providing  the  con- 
sent of  the  owner  can  be  obtained.  The  attachment  should  be  made 
to  the  trunk  of  the  tree  as  shown  in  Fig.  169,  but  may,  in  exceptional 
cases,  be  fastened  to  a  live  limb  close  to  the  trunk,  as  indicated  in 
Fig.  170,  providing  the  limb  is  at  least  five  inches  in  diameter.  The 
trunk  or  the  limb  of  the  tree  should  always  be  protected  from  injury 
by  strips  of  hard  wood,  each  strip  being  about  one  inch  thick,  12  inches 
long  and  not  over  two  inches  wide.  The  guy  wire  is  then  looped  about 
the  tree  and  fastened  with  a  guy  clamp.  The  provision  of  these 
blocks  under  the  guy  wire  prevents  injury  of  the  bark,  which  would 


294 


TOLL  TELEPHONE  PRACTICE 


FIG.  169.  —  Guying  to  Tree  Trunks. 


FIG.  170.  —  Guying  to  Tree  Limbs. 


LINE  CONSTRUCTION 


295 


otherwise  suffer  severely  from  abrasion,  possibly  to  the  extent  of 
killing  the  tree.  The  protection  of  the  property  of  abutting  owners 
can  never  be  too  seriously  considered,  as  right  of  way  and  trimming 
privileges  are  seldom  easily  obtained,  and  it  requires  but  a  few  instances 
of  real  damage  to  make  the  securing  of  these  privileges  well-nigh 
impossible.  Nothing  is  more  detrimental  to  the  telephone  company 
than  to  be  on  hostile  and  unfriendly  terms  with  the  property  owners 
that  adjoin  the  right  of  way. 

When  it  is  convenient  or  necessary,  guys  may  be  attached  to  solid 
rock  as  shown  at  A  in  Fig.  171.     Care  should  be  given  to  the  selection 


FIG.  171.  —  Rock  Guying. 

of  rock  which  is  in  good  physical  condition.  If  the  rock  has  a  tend- 
ency to  split,  an  eyebolt  should  be  used  which  has  a  tensile  strength 
of  60,000  pounds  per  square  inch,  placed  as  shown  at  B  in  Fig.  171. 
The  depth  to  which  this  bolt  should  be  embedded  is  regulated  by  the 
nature  of  the  rock.  It  is  advisable  to  pour  sulphur  or  lead  into  the 
hole  to  provide  a  firm  anchorage. 

The  rock  anchor  shown  in  Fig.  172  is  one  manufactured  by  the 
Miller  Anchor  Company.  The  rod  A  is  securely  fastened  to  the 
smooth  piece  B,  and  B  constitutes  one-half  of  a  cylinder  of  which  C 
is  the  other  half.  B  and  C  are  both  wedge-shaped,  the  tapers  on  the 
two  pieces  being  in  opposite  directions.  The  part  C  is  corrugated  so 
that  it  will  take  a  firm  hold  in  the  rock,  while  B  has  a  smooth  surface 


296 


TOLL  TELEPHONE  PRACTICE 


which  allows  it  to  slide  readily.  This  anchor  is  best  installed  by 
tying  the  piece  C  to  A  and  B  and  then  inserting  them  in  a  hole  drilled 
just  large  enough  for  a  sliding  fit.  The  wedge  C  is  then  driven  down 

slightly  so  that  the  corrugations  will 
take  a  firm  hold  in  the  rock.  If  tension 
is  applied  to  the  rod  A  the  anchor  will 
tighten,  due  to  the  wedge-shaped  pieces; 
hence  the  greater  the  load  the  tighter 
they  will  be  held  in  position.  These 
anchors  will  stand  a  stress  of  15,000 
pounds. 

On  all  toll  lines  exposed  to  sleet  and 
wind  loads,  a  regular  system  of  storm 
guying  should  be  utilized  to  prevent  the 
wrecking  of  long  sections  of  line.  The 
practice  -  of  storm  guying  has  become 
quite  general  on  heavy  lines,  and  in 
what  follows  the  methods  used  by  the 
American  Telephone  and  Telegraph  Com- 
pany are  described. 

On  straight  lines  carrying  one  cross- 
arm,  a  head  guy  and  a  side  guy  should 
be  placed  at  least  once  every  mile. 

On  a  line  containing  two  cross-arms 
and  more  than  ten  wires  the  line  should 
be  double  head  guyed  and  double  side 
guyed  every  mile. 

On  a  line  containing  three  cross-arms 


FIG.  172.  —  Miller  Rock  Anchor. 


and  more  than  20  wires  the  line  should  be  double  head  guyed  and 
•double  side  guyed  every  half  mile. 

On  a  line  containing  four  cross-arms  and  more  than  30  wires  the 
guys  on  corner  poles  should  be  doubled.  The  line  should  be  double 
side  guyed  every  quarter  mile,  double  head  guyed  every  half  mile, 
and  additional  side  guys  should  be  used  whenever  necessary. 

These  requirements  may  seem  excessive,  but  experience  proves 
their  ultimate  economy  in  zones  where  combined  wind  and  sleet  are 
regularly  encountered. 

All  terminal  poles,  and  those  which  support  long  spans  of  say 
200  feet  or  more,  should  be  specially  guyed.  In  general  the  adjacent 


LINE  CONSTRUCTION 


297 


poles  should  be  head  guyed  to  the  terminal  pole;  and  the  terminal 
pole,  whenever  it  is  possible,  should  be  side  guyed  in  both  directions. 
All  curves  and  corners  should  be  thoroughly  guyed  as  shown  in  Fig. 
173.  It  will  be  noted  that  the  arrangement  at  B  shows  the  corner 
guyed  in  two  directions  —  one  guy  to  relieve  the  longitudinal  pull  of 


FIG.  173.  —  Guying  at  Curves  and  Corners. 

the  straight  line  and  the  other  to  counteract  the  side  pull  at  the  turn. 
When  it  is  impossible  to  guy  in  this  manner,  the  method  shown  at  A 
in  the  same  figure  may  be  employed.  All  poles  on  a  curve  should  be 
guyed,  as  shown  at  C,  owing  to  the  fact  that  the  direction  of  the  line 
.wires  is  continually  changing.  When  the  radius  of  the  curve  is  large 
and  there  are -few  wires,  it  may  be  sufficient  to  rake  the  poles;  but  in 
most  cases  guying  is  economical  or  even  necessary. 

Bracing  is  superior  in  general  to  guying,  but  sometimes  more  ex- 
pensive in  respect  to  first  cost.     One  of  the  feasible  methods  is  shown 


298 


TOLL  TELEPHONE  PRACTICE 


in  Fig.  174.  It  is  well  to  set  the  butts  of  the  braces  from  three  to  four 
feet  in  the  ground  and  anchor  them  in  such  a  manner  as  to  distribute 
the  weight  and  reduce  the  pressure  per  unit  area. 


FIG.  174.  —  Double  Pole  Braces. 

Miscellaneous  Material.  —  Stranded  wire  rope  is  manufactured 
especially  for  guying  purposes  and  is  usually  composed  of  seven  No.  12 
B.  W.  G.  galvanized  steel  wires.  The  external  diameter  of  this  rope 
varies  from  one-quarter  to  three-eighths  of  an  inch;  the  minimum 
breaking  strength  should  be  6000  pounds.  The  strands  should  be 
free  from  scales,  inequalities,  splints,  flaws  and  all  other  imperfections, 
arid  should  be  of  circular  section  with  uniform  diameter.  Each 
strand  should  be  drawn  in  one  continuous  length  and  free  from  factory 
joints. 

All  guy  strands  and  all  iron  and  steel  fittings  should  be  heavily 
galvanized  to  prevent  corrosion,  or  delay  its  appearance  as  much  as 
possible.  The  galvanizing  should  consist  of  a  coating  of  zinc,  evenly 
and  uniformly  applied,  and  should  adhere  firmly  to  the  surface  of  the 
iron  or  steel. 


LINE  CONSTRUCTION 


299 


Any  specimen  should  be  capable  of  withstanding  the  following  test. 
The  sample  should  be  immersed  in  a  saturated  solution  of  copper 
sulphate  for  one  minute,  then  thoroughly  washed  in  water  and  wiped 
dry.  This  process  should  be  repeated  several  times.  If,  after  the  fourth 
immersion,  there  should  be  a  copper-colored  deposit  on  the  sample, 
or  the  zinc  should  have  been  removed,  the  lot  from  which  the 
sample  was  taken  should  be  rejected.  The  solution  should  have  a 


FIG.  175.  —  Three-bolt  Guy  Clamp. 

specific  gravity  of  1.185  at  7°°  F.  While  a  sample  is  being  tested, 
the  temperature  of  the  solution  should  at  no  time  be  less  than  60° 
nor  more  than  80°  F.  The  threads  on  all  iron  or  steel  bolts,  on  which 
nuts  are  to  be  used,  should  be  galvanized  in  the  following  manner. 
The  threads  should  first  be  cut  with 
a  small  die,  galvanized,  and  then 
recut  with  a  die  of  standard  size, 
which  should  leave  a  coating  of  zinc 
on  the  threads. 

There  are  several  methods  of  fas- 
tening a  guy  strand.  One  way  is 
by  means  of  wr ought-iron  clamps, 
but  the  malleable  iron  three-bolt 
clamp  shown -in  Fig.  175  is  superior; 
there  the  bolts  are  made  of  high- 
carbon  steel.  Whenever  it  is  desired 
to  attach  the  guy  wire  to  an  eye,  as 


FIG.  176.  —  Standard  Thimble. 


in  an  anchor  rod,  for  example,  a  thimble  like  that  shown  in  Fig.  176 
should  be  used  to  interlink  the  guy  rope  and  the  rod.  When  the 
guy  wire  is  attached  to  a  stub  the  proper  method  of  fastening  is 
to  pass  the  rope  twice  around  the  pole  and  then  through  a  clamp. 


3oo 


TOLL  TELEPHONE  PRACTICE 


The  use  of  clamps  is  recommended  because  they  can  be  easily  removed 
without  waste  of  material,  which  is  not  possible  with  a  wrapped 
connection. 

Of  the  material  used  in  ordinary  lines  we  have  now  discussed  all 
but  the  insulators.  These  are  constructed  either  of  porcelain  or 
glass,  of  which  the  latter  is  used  almost  universally  in  this  country. 
The  leakage  is  made  a -minimum  by  making  the  diameter  of  the  insu- 
lator as  small  as  possible,  and  by  adding  to  the  length  of  the  leakage 
path  by  means  of  two  or  more  petticoats.  This  increases  the  insula- 
tion resistance,  which  depends  greatly  upon  the  surface  accumulations 
of  dirt  and  other  foreign  matter;  the  resistance  falls  materially  in 
foggy  or  rainy  weather.  The  general  form  of  the  standard  line  insu- 
lator is  shown  at  B  in  Fig.  177,  while  an  insulator  with  a  double  petti- 


"Fic.  177.  —  Standard  Line  Insulator  and  Two-piece  Transposition  Insulator. 

coat  is  shown  at  B  in  Fig.  178.  This  latter,  in  addition  to  the 
advantage  of  having  a  long  leakage  path,  has  also  the  advantage  that 
the  second  petticoat  is  completely  protected  from  falling  rain.  The 
standard  two-piece  transposition  insulator  used  by  the  American 
Telephone  and  Telegraph  Company  is  shown  at  A  in  Fig.  177.  This 
insulator  is  much  heavier  and  larger  than  the  ordinary  line  insulator 


LINE   CONSTRUCTION 


and,  as  previously  stated,  requires  an  extra  long  pin.  Most  of  the 
independent  telephone  companies  use  the  one-piece  transposition  insu- 
lator as  shown  at  A  in  Fig.  178. 


FIG.  1 78.  —  Double  Petticoat  Line  Insulator  and  One-piece  Transposition  Insulator. 

Wire  Stringing.  —  The  remaining  feature  of  construction  to  be  con- 
sidered is  wire  stringing.  When  only  one  or  two  wires  are  to  be 
strung,  one  end  of  the  wire  is  attached  to  the  cross-arm  at  the  be- 
ginning of  the  section,  and  the  wire  is  unreeled  along  the  pole  route, 
using  a  pay-out  reel  mounted  on  a  hand  barrow  as  shown  in  Fig.  179. 


FIG.  179.  —  Pay-out  Reel. 


FIG.  1 80.  —  Wagon  Pay-out  Reel. 


However,  several  toll  circuits  are  usually  strung  at  a  time  and  the 
wire  wagon  and  running  board  are  employed.  The  wire  wagon  is 
very  solidly  constructed  and  carries  wire  reels  as  shown  in  Fig.  180, 


302  TOLL  TELEPHONE  PRACTICE 

five  on  each  side  of  the  wagon.  At  the  back  of  the  wagon  is  placed 
a  wooden  bar  in  which  ten  guides  are  cut ;  these  guides  serve  to  sepa- 
rate the  wires  and  thereby  greatly  reduce  the  trouble  in  handling 
them.  When  the  wires  have  been  passed  through  the  guides  they 
are  fastened  to  a  running  board  such  as  that  shown  in  Fig.  181.  This 
consists  of  a  triangular  piece  of  iron  to  one 
corner  of  which  is  attached  a  ring  and  swivel. 
The  side  of  the  triangle  opposite  the  pulling 
ring  is  perforated  with  eleven  holes  to  receive 
the  wires.  The  wires  may  be  fastened  directly 
to  the  bar,  or,  as  often  the  case,  they  can  be 
secured  by  snaps  so  as  to  facilitate  rapid  re- 
moval at  each  pole  of  the  five  wires  which  must 
pass  around  the  pole  on  the  side  opposite  from 
the  pulling  rope.  This  is  not  necessary  on  new 
work,  however,  for  then  the  wires  should  be 

pulled  °Ver  the  t0p  cross-arm  and  then  dr°PPed 
into  place.     The  eleventh  hole  in  the  running 

board  is  provided  so  that  a  suitable  "  fish  wire  "  may  be  pulled 
through,  by  means  of  which  the  hauling  rope  can  be  pulled  back  for 
the  next  group  of  wires.  A  suitable  wire  or  a  rope  should  be  at- 
tached to  one  end  of  the  running  board  to  prevent  it  from  twisting 
and  turning,  as  otherwise  the  wires  might  twist  or  tangle.  In  haul- 
ing the  wire,  a  strong  rope  which  has  been  previously  passed  over 
the  cross-arms  from  the  far  end  of  the  section  is  attached  to  the 
pulling  ring. 

The  wagon  with  the  pay-out  reels  is  stationed  at  the  beginning  of 
the  run  and  a  team  of  horses,  at  the  far  end  of  the  section,  is  hitched 
to  the  pulling  rope.  A  man  is  stationed  on  each  pole  to  lift  the  run- 
ning board  over  the  cross-arm  and  to  separate  and  place  the  wires. 
In  this  manner  ten  wires  can  be  strung  in  one  haul.  When  wires  are 
strurig  on  the  lower  cross-arm  it  is  well  to  use  two  running  boards, 
attaching  five  wires  to  each  and  thus  avoiding  the  necessity  of  passing 
five  of  the  wires  around  each  pole,  as  would  be  the  case  if  all  ten  wires 
were  attached  to  one  running  board.  The  two  running  boards  can 
readily  be  pulled  in  one  haul,  a  separate  rope  being  attached  to  each 
board.  After  about  one-half  mile  has  been  strung  as  described,  the 
wires  should  be  stretched  and  tied.  The  stretching  is  accomplished 
by  means  of  a  "  come-along  "  (Fig.  182)  and  pulleys.  The  "  come- 


LINE  CONSTRUCTION 


303 


along  "  shown  in  the  figure  has  met  with  general  satisfaction  for 
pulling  hard-drawn  copper,  due  to  the  fact  that  the  jaws  are  smooth, 
straight  and  parallel,  thus  avoiding  to  the  greatest  possible  extent 
the  likelihood  of  nicking  the  wire.  This  is  of  great  importance,  and 


FIG.  182.  —  Come- Along. 

it  should  also  be  remembered  that  a  kink  should  never  be  allowed  to 
remain  in  hard-drawn  copper  wire.  The  proper  remedy  is  to  cut  out  the 
kink  and  make  a  sleeve  joint.  In  using  the  "  come-along  "  the  ten- 
sion is  applied  at  the  eyelet  and  it  will  be  noted  from  the  construction 
that  as  the  tension  increases,  the  hold  on  the  wire  correspondingly 
increases.  When  the  tension  is  removed  the  jaws  of  the  appliance 


FIG.  183.  —  Pulling  Up  Line  Wire. 

are  automatically  opened.  In  stretching  the  wire,  conductors  of  the 
same  size  and  material  may  be  pulled  up  together.  If  six  wires 
are  being  pulled  up,  a  three-sheave  block  should  be  used;  for  eight 
wires,  a  four-sheave  block;  and  for  ten  wires  a  five-sheave  block,  as 
shown  in  Fig.  183. 


304 


TOLL  TELEPHONE  PRACTICE 


After  the  wire  is  stretched  to  the  proper  tension  and  deflection,  the 
man  handling  the  "  come-alongs  "  and  pulleys  gives  the  signal  to  the 
men  on  the  poles  to  "  tie  in,"  and  they  then  proceed  to  permanently 
fasten  the  wires  to  the  insulators.  It  should  be  remembered  in  this 
connection  that  hard-drawn  copper  wire  is  likely  to  stretch,  and 
several  months  after  a  new  line  has  been  built  the  deflections  may 
have  increased  considerably. 

The  best  method  of  tying  copper  wire  to  an  insulator  is  shown  in 
detail  at  A  in  Fig.  184.  The  tie  wire  and  the  line  wire  are  laid  in 

A«T-&T.Co'S.  METHOD 


POSTAL   TELEGRAPH    METHOD 


FIG.  184.  —  Method  of  Tying  Wire  to  Insulator. 

the  groove  and  the  tie  is  passed  Once  around  the  insulator.  One  end 
of  the  tie  wire  is  now  brought  down  over  the  line  wire,  while  the  other 
end  is  brought  up  under  it,  in  the  opposite  direction.  The  two  pro- 
jecting ends  are  then  given  five  turns  around  the  line  wire,  and  the 
tie  is  complete  as  shown  in  the  central  view  in  the  figure.  The  tie 
wire  should  be  of  soft  copper  of  the  same  size  as  the  line  wire.  For 
No.  14  N.  B'.  S.  G.  wire  the  ties  should  be  17  inches  in  length,  for 
No.  12  N.  B.  S.  G.  wire,  19  inches  and  for  No.  8  B.  W.  G.  wire,  24 
inches.  The  standard  method  of  tying  iron  wire  is  shown  at  B  in 
Fig.  184. 
The  proper  location  of  the  line  wires  with  respect  to  the  insulators 


LINE  CONSTRUCTION 


305 


for  tangent  sections  and  curves  is  shown  at  A  and  B,  respectively, 
in  Fig.  185.  It  will  be  observed  that  on  tangent  or  straightaway 
sections  the  line  wires  on  the  four  outer  pins  are  placed  on  the  sides 


FIG.  185.  —  Location  of  Wire  on  Insulators. 

of  the  insulators  next  to  the  pole,  while  on  the  two  inner  insulators 
the  line  wires  are  located  in  the  reverse  position.  At  curves  the  line 
wire  should  always  be  placed  on  the  side  away  from  the  center  of  the 
curve,  so  that  the  stress  due  to  the  angle  in  the  line  will  be  exerted 


FIG.  186.  —  Dead-Ending. 

on  the  pin  and  not  on  the  tie.  When  the  wire  is  attached  to  the  last 
insulator  on  the  line,  or  terminated  at  some  intermediate  point, 
generally  termed  "  dead-ending,"  it  should  be  looped  around  the 
insulator  as  illustrated  in  Fig.  186.  The  wire  should  always  be  looped 


306 


TOLL  TELEPHONE  PRACTICE 


as  shown,  and  should  never  be  wound  around  the  insulator.  A  dead- 
end can  be  fastened  by  means  of  a  half  sleeve,  as  shown  at  A,  or  the 
wire  may  bejvrapped  about  itself  for  about  ten  turns  as  shown  at  B. 
When  another  wire  is  to  be  joined  to  the  dead-ended  line,  it  is  well  to 
allow  enough  projection  through  the  joint  so  that  the  connection  can 
be  made  to  the  loose  end,  instead  of  the  stressed  conductor,  or  span. 
When  two  lines  are  thus  dead-ended  with  the  intention  of  making  a 
through  connection,  it  is  best  to  dead-end  them  on  a  single  cross-arm 
instead  of  the  double  arm  often  used.  For  this  purpose  a  transposi- 
tion insulator  is  generally  employed,  one  wire  being  dead-ended  in 
the  upper  groove  and  the  other  in  the  lower.  This  method  is  advis- 
able because  it  reduces  the  pin  stress  to  a  minimum,  as  the  pull  due 
to  the  tension  of  the  wire  in  one  direction  is  practically  counteracted 
by  the  tension  in  the  opposite  direction.  When  double  cross-arms 
are  used  this  is  not  the  case,  and  the  pins  must  support  the  full  tensions 
of  the  spans. 

All  joints  in  copper  should  be  made  by  means  of  sleeves,  a  typical 
example  of  which  is  the  Cook  joint  shown  in  Fig.  187.     There  are 


FIG.  187.  —  Cook  Wire  Joint. 

many  forms  of  these  joints  on  the  market  but  they  all  operate  on 
about  the  same  principle,  so  a  description  of  one  will  suffice.  The 
old  practice  of  making  a  twisted  splice,  with  the  use  of  solder,  should 
never  be  followed.  In  making  a  sleeve  joint,  each  end  of  the  wire 
should  be  passed  through  the  sleeve  so  as  to  project  about  one-quarter 
of  an  inch.  A  tie  wrench  or  connector  is  placed  at  each  end  of  the 
sleeve,  with  about  one-quarter  of  an  inch  projecting,  and  the  required 
number  of  twists  is  then  given.  The  sleeves  are  made  for  the  different 
sizes  of  wire  and  the  number  of  twists  varies  accordingly;  thus  the 
sleeve  for  a  No.  14  or  a  No.  12  N.  B.  S.  G.  wire  should  have  four  com- 
plete twists,  while  a  No.  8  B.  W.  G.  wire  requires  four  and  one-half 
twists. 


CHAPTER  XVIII 
ELECTRICAL  REACTIONS  IN   TELEPHONE  LINES 

TOLL-LINE  construction,  outside  of  urban  districts,  is  comprised 
almost  wholly  of  open-wire  circuits  of  the  type  previously  considered. 
Circuits  of  the  cable  type  are  much  less  efficient  in  general  than  open 
wires  and  hence  undesirable  in  long  toll  lines.  But  cable  construction 
is  often  unavoidable;  this  holds  true  in  nearly  every  case  at  city  ter- 
minals or  terminal  offices,  where  several  miles  of  underground  cable 
is  quite  common.  Submarine  crossings  at  rivers  and  bays  are  also 
unavoidable  in  many  instances.  In  general,  the  total  length  of  cable 
should  be  made  a  minimum,  in  order  to  secure  an  adequate  standard 
of  transmission  at  a  minimum  of  cost. 

The  development  of  the  loading  art  has  relieved  the  cable  diffi- 
culties to  some  extent,  but  not  completely.  There  are  many  sections 
of  cable  in  a  long  line  of  open  wire  which  cannot  be  loaded  efficiently. 
Toll  cables  of  special  design  are  very  essential  in  securing  maximum 
transmission  efficiency  at  minimum  cost. 

In  the  early  stages  of  toll  development  it  was  permissible  to  locate 
a  toll  office  well  within  the  limits  of  a  fairly  large  city  without  the 
use  of  much  cable,  but  this  condition  now  rarely  exists  because  of  the 
general  practice  of  requiring  all  wires  to  be  placed  underground. 
Following  the  requirements  last  mentioned  it  became  the  policy  to 
situate  toll  offices  outside  of  the  underground  limits,  often  near  the 
city  outskirts.  Since  the  introduction  of  special  toll  cables,  and 
loading,  however,  the  policy  has  been  reversed  to  some  extent  and 
the  more  recent  large  installations  have  been  located  near  the  center 
of  local  distribution. 

In  dealing,  then,  with  toll  lines  of  the  general  type,  there  are  two 
distinct  classes  of  circuits  to  consider,  one  comprised  of  cable  and  the 
other  of  open  wire.  The  properties  of  these  two  kinds  of  circuits  are 
essentially  different,  and  hence  their  reactions  are  different  also.  In 
order  to  comprehend  their  actions  fully,  it  is  necessary  to  consider 
the  most  general  type  of  circuit  first. 

307 


308  TOLL  TELEPHONE  PRACTICE 

General  Properties.  —  The  general  type  of  toll  circuit,  whether 
grounded  or  metallic,  possesses  four  distinct  properties.  These  will 
be  explained  from  the  standpoint  of  metallic  circuits,  which  is  the 
only  suitable  type  for  general  service  and  particularly  for  long-distance 
service.  These  four  properties  are  resistance,  inductance,  capacity 
and  leakage. 

Resistance  is  so  well  understood  that  it  needs  no  explanation.  It 
is  analogous  to  friction  in  mechanics  and  wastes  energy  in  proportion 
to  the  product  of  the  square  of  the  current,  the  resistance  and  the 
time;  this  lost  energy  appears  as  heat  and  is  radiated  to  the  atmosphere 
or  surrounding  bodies.  It  is  necessary  to  distinguish,  however,  be- 
tween true  or  ohmic  resistance  and  apparent  or  effective  resistance. 
There  is  no  difference  between  the  two  for  continuous  and  low-fre- 
quency alternating  currents,  with  conductors  of  the  size  used  in 
telephony.  But  with  the  relatively  high  frequencies  reached  in 
telephony,  the  difference  becomes  appreciable  and  the  effective 
resistance  is  the  greater.  This  is  due  to  a  lack  of  penetration  of  the 
current  to  the  center  or  core  of  the  conductor,  and  to  local  or  eddy 
currents  in  the  conductor;  when  iron  is  employed,  hysteresis  is  also 
a  factor.  The  increase  of  effective  over  true  resistance  is  termed  the 
skin  effect.  This  effect  is  not  of  consequence  with  copper  wires  until 
the  higher  frequencies  are  considered,  unless  the  wires  are  unusually 
large;  but  with  iron  wires  it  is  very  prominent,  because  of  their  large 
magnetic  permeability.  In  general  the  effect  increases  with  the 
frequency,  the  size  of  the  conductor  and  its  permeability.  A  mathe- 
matical discussion  of  the  subject  is  too  complex  for  presentation  here, 
but  it  has  been  exhaustively  treated  by  several  eminent  authorities 
whose  writings  may  be  consulted. 

Inductance  is  the  property  of  a  conductor  which  exists  by  virtue 
of  the  fact  that  every  electric  current  establishes  a  magnetic  field. 
When  the  current  is  variable,  the  field  varies  also,  and  induces  in  the 
conductor  a  counter  E.M.F.,  which  absorbs  or  neutralizes  a  com- 
ponent of  the  impressed  E.M.F.  and  causes  the  current  to  lag  in  time 
or  phase  behind  the  impressed  E.M.F.  The  absolute  value  of  the 
inductance  is  the  product  of  the  number  of  lines  of  magnetic  flux 
and  the  number  of  turns  of  the  conductor  which  conveys  the  exciting 
current  and  with  which  they  are  linked;  or  expressed  more  briefly, 
it  is  the  total  number  of  flux  linkages  with  the  circuit.  Inductance, 
then,  causes  the  current  to  lag  behind  its  impressed  E.M.F.  and 


ELECTRICAL  REACTIONS   IN  TELEPHONE  LINES  309 

consumes  a  component  of  the  E.M.F.  It  does  not,  however,  consume 
energy.  The  instantaneous  value  of  the  energy  stored  in  a  pure 
inductance  whose  coefficient  of  self-induction  is  L,  when  the  current 
is  ij  is  \  L&-\  but  all  the  energy  which  the  inductance  receives  in  a 
given  half  -cycle  is  returned  during  the  succeeding  half  -cycle.  In- 
ductance coupled  in  series  with  resistance,  in  a  simple  series  circuit, 
gives  rise  to  the  impedance 

iy,    .  .  .  -..  ',  .  (i) 


where  p  is  2  irn  and  n  is  the  frequency  in  cycles  per  second.  The 
coefficient  of  self-induction  for  a  pair  of  suspended  parallel  wires, 
expressed  in  henrys  per  mile,  is 

L  =(0.1609  +  1.482  log^jio~3,   ...     .     .     .(2) 

where  d  is  the  distance  between  the  wires  and  r  is  their  radius,  in  like 
units.  This  formula  does  not  hold  when  -  is  small  or,  that  is,  for 

wires  near  together  in  comparison  with  their  common  radius;  cable 
circuits  form  a  case  in  point,  but  there  the  inductance  is  so  small  as 
to  be  negligible. 

Capacity  is  the  property  of  a  circuit  which  exists  by  reason  of  the 
fact  that  the  two  opposite  sides  of  the  circuit  form  a  condenser.  When- 
ever the  terminals  of  the  circuit  are  connected  to  a  source  of  E.M.F.  , 
the  conductors  become  charged  like  the  opposite  plates  of  a  Leyden 
jar  or  condenser.  When  a  condenser  is  connected  to  a  source  of  con- 
tinuous E.M.F.,  a  transient  current  exists  while  the  condenser  is 
being  charged  and  then  ceases.  But  when  a  condenser  is  connected 
to  a  source  of  alternating  E.M.F.,  it  alternately  charges  and  discharges 
with  the  alternations  of  impressed  E.M.F.  and  in  effect  an  alternating 
current  flows  through  it.  At  any  instant  the  charge  is  proportional 
to  the  product  of  the  capacity  and  the  instantaneous  E.M.F.  But 
the  current  is  proportional  to  the  rate  of  change  of  the  charge  with 
respect  to  the  time,  and  is  therefore  90°  ahead  of  the  impressed  E.M.F. 
if  the  latter  is  periodic  and  sinusoidal.  The  condenser,  like  an  in- 
ductance, consumes  a  component  of  the  impressed  E.M.F.,  but  instead 
of  causing  the  current  to  lag,  makes  it  leading.  Similarly  it  consumes 
no  energy.  At  any  instant  the  energy  stored  in  the  condenser  is 
\  Ce2,  where  C  is  the  coefficient  of  capacity  and  e  is  the  instantaneous 


310  TOLL  TELEPHONE  PRACTICE 

value  of  E.M.F.  But  the  energy  which  the  condenser  receives  in 
one  half  -cycle  is  returned  in  the  next,  or,  in  other  words,  charge  and 
discharge  are  equal.  The  impedance  due  to  simple  resistance  and 
capacity  in  series  is  given  by 


where  pis2wn  as  before.     The  capacity  of  a  pair  of  parallel  suspended 
wires  in  microfarads  per  mile  is 


i          " 

log- 

where  d  and  r  have  the  previous  meanings.  This  formula  holds  only 
when  -is  large,  and  therefore  does  not  apply  to  cable  circuits.  In 

the  latter  case,  however,  the  capacity  depends  in  addition  upon  the 
specific  inductive  capacity  of  the  insulation  and  it  is  more  direct  to 
find  the  capacity  by  actual  measurement. 

Leakage  is  not  a  property  of  the  wires  themselves,  but  of  the  insu- 
lation. It  is  commonly  spoken  of  in  terms  of  leakage  or  insulation 
resistance.  In  cable  circuits  it  depends  upon  the  specific  resistance 
of  the  insulating  material,  which  should  be  as  high  as  possible;  in 
well-made  cables  the  leakage  should  be  negligible.  In  lines  of  open 
wire,  dependence  for  insulation  is  placed  upon  the  insulating  supports, 
of  glass  or  porcelain.  When  the  insulators  are  made  of  high-grade 
material,  the  insulation  depends  in  great  part  upon  the  surface  con- 
ditions, which  in  turn  vary  in  a  large  degree  with  weather  conditions. 
Leakage,  or  leakage  resistance,  absorbs  energy  and  dissipates  it  as 
heat,  after  the  manner  of  resistance  of  any  kind. 

The  properties  of  a  telephone  circuit,  consisting  of  a  pair  of  very 
long  parallel  wires,  are  not  like  those  of  simple  resistances,  inductances 
and  capacities.  This  arises  from  the  fact  that  resistance,  inductance, 
capacity  and  leakage  in  a  telephone  line  are  uniformly  distributed, 
whereas  in  the  usual  theoretical  treatment  of  alternating  current 
problems  they  are  taken  as  concentrated  or  lumped.  This  difference 
is  of  fundamental  importance  and  alters  the  whole  theoretical  treat- 
ment. The  resistance  and  the  inductance  are  serially  connected  with 
respect  to  the  circuit  and  act,  for  any  small  portion  of  the  circuit, 
just  as  simple  or  concentrated  resistance  and  inductance  would  act. 


ELECTRICAL  REACTIONS  IN  TELEPHONE  LINES  311 

The  capacity  and  the  leakage  are  connected  in  shunt  with  the  circuit 
and  divert  current  from  it;  the  capacity  and  the  leakage  are  also  in 
shunt  or  parallel  with  each  other. 

The  complete  theoretical  treatment  of  such  a  circuit  will  not  be 
given,  but  the  general  subject  of  attenuation  will  be  explained  briefly. 
Attenuation  implies  the  progressive  loss  of  amplitude  or  strength 
which  a  wave  of  current  or  E.M.F.  suffers  in  traveling  along  the 
circuit  from  the  origin  to  the  distant  terminal.  In  general,  neglecting 
reflection  at  the  terminals,  the  strength  of  a  current  wave  of  initial 
strength  I0,  when  it  has  traveled  a  distance  /  from  the  outgoing  end 
or  terminal,  is 

/,-/.«-*     ........    (5) 

where  e  is  the  base  of  the  Napierian  system  of  logarithms  and  p  is  the 
attenuation  constant,  /  being  in  miles. 


(6) 


where  R,  L,  and  C  are  the  respective  constants  per  mile  and  p  is 
2  TTH.  The  minimum  rate  of  attenuation  depends  upon  the  minimum 
value  of  £,  the  attenuation  constant.  Obviously  this  value  of  0 
corresponds  to  minimum  values  of  R  and  C  and  a  maximum  value  of 
L,  or  minimum  resistance  and  capacity  and  maximum  inductance. 
It  is  also  true  that  the  leakage  should  be  a  minimum.  An  inspection 
of  the  formula  for  0  also  shows  that  the  attenuation  increases  with 
the  frequency. 

Efficient  transmission  implies  efficiency  with  respect  to  both  volume 
and  quality.  In  telephony  the  actual  line  current  is  very  complex 
because  so  many  frequencies  are  present.  The  range  of  frequency  is 
ordinarily  accepted  as  from  100  to  2000  cycles  per  second.  Since 
the  rate  of  attenuation  increases  with  the  frequency,  it  is  evident 
that  all  the  components  of  a  complex  wave  will  not  be  transmitted 
with  like  efficiency,  but  those  of  highest  frequency  will  be  attenuated 
most.  . 

The  timbre  or  quality  of  sound  depends  upon  the  pitch  and  the 
relative  intensity  of  the  component  partials,  and  in  order  to  fully 
preserve  the  quality  of  transmitted  speech,  it  is  evident  that  the 
component  frequencies  of  any  complex  wave  must  be  transmitted 
with  equal  rates  of  attenuation.  Where  this  is  not  the  case,  distor- 
tion, or  impaired  quality,  will  unavoidably  occur.  The  effect  of  dis- 


312  TOLL  TELEPHONE  PRACTICE 

tortion  is  a  matter  of  degree,  however,  and  there  is  a  noticeable 
difference  between  circuits  in  cable  and  those  of  open  wire. 

Cable  Circuits.  —  In  circuits  of  the  cable  type  the  inductance  is 
practically  negligible  and  the  formula  for  the  attenuation  constant  is 


(7) 


This  gives  the  foundation  of  the  so-called  KR  law,  where  K  is  the 
symbol  for  capacity  and  R  for  resistance.  Assuming  a  given  fre- 
quency, it  is  evident  that  two  unlike  cables,  of  equal  length,  will  cause 
the  same  attenuation  if  the  product  KR  in  the  two  cases  is  the  same, 
and  knowing  by  experience  the  limit  of  length  of  a  cable  of  given 
resistance  and  capacity,  a  limiting  value  of  KR  can  be  found.  Evi- 
dently 

(8) 


IR  is  the  total  cable  resistance  and  1C  the  total  capacity,  so  that 
the  product  of  total  resistance  and  total  capacity  is  the  total  KR, 
on  which  a  limit  can  be  placed  for  efficient  transmission  and  by  means 
of  which  dissimilar  cables  can  be  compared.  Cable  efficiency  is  obvi- 
ously increased  by  diminishing  the  resistance  and  the  capacity  per  mile. 

The  first  cables  generally  used  in  toll  lines  were  those  which  were 
standard  for  local  systems,  or  No.  19  B.  &  S.  gauge,  with  a  mutual 
capacity  of  0.054  microfarad  per  mile.  High-capacity  cable  of  the 
same  gauge  has  a  mutual  capacity  of  0.080  microfarad  per  mile. 
No.  22  B.  &  S.  gauge,  with  a  capacity  of  0.069  microfarad,  has  been 
used  a  great  deal  for  local  work  and,  in  some  cases,  in  toll  lines.  About 
the  year  1900  a  good  deal  of  development  work  was  commenced  on  toll 
cables  of  higher  efficiency.  It  is  impracticable  to  reduce  the  capacity 
of  cables  of  larger  gauge  to  any  appreciable  extent,  and  the  special  toll 
cable  is  practically  like  the  early  types,  except  that  it  has  larger 
conductors. 

The  insulation  used  on  the  conductors  in  ,  these  cables  consists  of  a 
loose  wrapping  of  very  porous  dry  paper,  which  permits  the  inclosure 
of  the  greatest  possible  amount  of  dry  air.  This  is  very  beneficial, 
inasmuch  as  air,  next  to  hydrogen,  possesses  the  lowest  specific  in- 
ductive capacity  of  any  known  substance.  The  two  wires  which 
form  each  pair  are  twisted  together,  the  length  of  a  complete  twist 
being  not  greater  than  three  inches.  These  twisted  pairs  are  then 


ELECTRICAL  REACTIONS  IN  TELEPHONE  LINES  313 

formed  into  a  core  arranged  in  reversed  layers,  and  the  whole  covered 
with  a  layer  of  heavy  tough  paper.  Around  this  paper  covering  is 
placed  a  sheath  composed  of  lead  and  tin,  which  should  have  a  thick- 
ness of  at  least  one-eighth  of  an  inch.  In  the  manufacture  of  the 
cable,  the  core  is  thoroughly  baked  before  it  is  inclosed  in  the  lead 
sheath,  thus  excluding  all  moisture.  A  cable  thus  constructed  is 
known,  therefore,  as  the  dry-core  cable.  Due  to  the  fact  that  the 
insulation  and  capacity  of  the  cable  depend  upon  keeping  the  core 
perfectly  dry,  the  sheath  at  either  end  should  be  hermetically  sealed 
at  all  times,  except  when  it  is  necessary  to  expose  the  conductors  for 
splicing  or  other  work.  The  sheath  should  be  sealed  up  immediately 
after  all  work  is  completed,  due  caution  being  exercised  to  drive  out, 
by  a  suitable  bath  in  hot  paraffin,  any  moisture  that  may  have 
crept  into  the  exposed  end.  This  brief  description  applies  to  all  types 
of  dry-core  paper  cables.  The  size  of  conductor  varies  considerably; 
in  cables  for  local  work  conductors  as  small  as  No.  24  B.  &  S.  have 
been  employed,  while  toll  cables  have  been  made  with  conductors  as 
large  as  No.  10  B.  &  S.  Of  course  the  size  of  conductor  ranges  all 
the  way  between  these  limits,  depending  principally  upon  the  length 
of  the  cable,  the  total  length  and  character  of  the  circuit  and  the 
specified  standard  of  transmission.  The  capacity  depends  upon  how 
compactly  the  core  is  formed  and  can  be  varied  considerably. 

By  mutual  capacity  is  meant  the  capacity  between  each  wire  and 
its  mate,  in  distinction  from  grounded  capacity,  which  is  the  capacity 
of  one  conductor  measured  against  all  other 
conductors  grounded  on  the  sheath  of  the 
cable.  The  insulation  resistance  of  each 
wire  in  the  cable  should  be  at  least  100 
megohms  per  mile  when  the  cable  is  all 
laid,  spliced  and  ready  for  operation.  In 
Table  13  are  given  the  standard  require- 
ments of  a  number  of  trunk  and  toll-line 

,  ,  FIG.  188.  —  Cross  Section  of 

es'  Armored  Cable. 

The  type  of  cable  just  described  is  not 

suitable  for  submarine  crossings  in  navigable  waters,  where  it  may 
become  fouled  by  the  anchors  of  boats.  For  such  work  the  sheath 
is  surrounded  by  an  armor  of  steel  wire,  over  which  is  placed  a 
heavy  braid  thoroughly  impregnated  with  a  water-proofing  com- 
pound. These  cables  are  often  of  special  construction.  The  Ameri- 


TOLL  TELEPHONE  PRACTICE 


TABLE   13 
ELECTRICAL  PROPERTIES  OF  TRUNK  AND  TOLL  CABLES 


Size  of  Wire, 
B.  &  S.  Gauge. 

Number  of 
Pairs  in  Stand- 
ard Full  Size 
Cable,  2|  In. 
Inside  Diam- 
eter. 

Capacity  in  Microfarads  per 
Mile. 

Maximum 
Resistance  of 
Circuit  in 
Ohms  per  Mile 
at  68°  Fahr. 

Minimum. 

Maximum. 

IO 

35 

.072 

.080 

II 

13 

75 

.072 

.080 

22.5 

13 

55 

.066 

.074 

22.5 

H 

IOO 

.072 

.080 

30 

14 

80 

.066 

.074 

3° 

16 

.    150 

.      -074 

.081 

46 

16 

IOO 

.060 

.068 

46 

19 

300 

.074 

.081 

92 

!9 

1  80 

•054 

.060 

92 

can  Telephone  and  Telegraph  Company  have  used  a  type  shown  in 
Fig.  1 88;  there  A  is  the  regular  paper  insulation,  B  is  a  filling  of  as- 
phalt, C  is  a  wrapping  of  cotton,  D  is  the  lead  sheath  and  £  is  a 
wrapping  of  marlin;  over  the  whole  is  placed  the  steel  wire  armor,  F. 
The  detrimental  effect  of  capacity  is  felt  to  even  a  greater  extent  in 
submarine  cable  than  in  standard  underground  cable,  owing  to  the 
much  higher  specific  inductive  capacity. 

Uniformly  distributed  capacity  can  be  likened  to  an  infinite  number 
of  infinitesimal  condensers,  connected  in  shunt  with  the  line,  at  equal 
intervals.  For  experimental  purposes  an  artificial  line  can  be  con- 


KEY 


GALV 


MILLAMMETER 


FIG.  189.  —  Artificial  Line  with  Distributed  Capacity. 


structed  which  is  almost  an  exact  counterpart  of  a  real  line,  by  using 
small  lumped  resistances  and  capacities,  each  representing  but  a  very 
short  portion  of  an  actual  line.  This  is  indicated  in  Fig.  189.  When 
the  key  is  depressed  there  is  a  large  rush  of  current  to  charge  the  line, 
which  finally  decreases  to  a  steady  Ohm's  law  value.  The  current 


ELECTRICAL  REACTIONS  IN  TELEPHONE  LINES 


315 


arrives  at  the  distant  end  gradually  and  finally  builds  up  to  Ohm's 
law  value.  Fig.  190  shows  the  outgoing  current  from  the  battery  end, 
represented  by  the  curve  AB,  and  the  arrival  current  at  the  receiving 
end  is  shown  by  the  curve  CD.  The  slight  difference  between  B  and 
D  is  attributable  to  leakage.  If  the  closure  of  the  key  is  momen- 

A 


TIME: 


FIG.  190.  —  Outgoing  and  Incoming  Currents  on  a  Cable  with  a  Constant 
Impressed  E.M.F. 

tary,  the  current  curves  will  be  similar  to  those  shown  in  Fig.  191. 
If  a  succession  of  short  impulses  are  imparted  to  the  line,  such  as  A, 
B,  C  and  D  in  Fig.  192,  the  arrival  current  will  be  similar  to  that 
shown  at  £;  this  shows  how  the  impulses  trail  together  or  blur  during 
transmission,  which  is  a  species  of  distortion. 

In  a  cable  telephone  circuit,  like  that  shown  in  Fig.  193,  the  re- 
actions are  more  complex.  The  curves  in  Fig.  190  show  clearly  that 
the  line  must  become  fully  charged  before  the  full  current  strength 
arrives  at  the  distant  terminal.  But  when  a  rapidly  alternating 
E.M.F.  is  impressed  on  the  cable,  there  is  insufficient  time  during  a 
half  cycle  for  the  circuit  to  become  fully  charged,  and  hence  attenua- 
tion occurs.  The  potential  falls  from  point  to  point  along  the  circuit, 
due  to  the  ohmic  resistance;  and  the  current  falls  likewise,  owing  to  a 


316 


TOLL  TELEPHONE  PRACTICE 


B 


TIME 


TIME 

FIG.  191.  —  Effect  of  Closing  Key  Momentarily. 


TIME 


FIG.  192.  —  Effect  of  Succession  of  Impulses. 


FIG.  193.  —  Cable  Telephone  Circuit. 


ELECTRICAL  REACTIONS  IN  TELEPHONE  LINES       317 

constant  absorption  which  is  the  result  of  charging  the  elementary  or 
infinitesimal  condensers.  The  resultant  or  compound  effect  produces 
very  rapid  attenuation.  At  the  same  time,  the  wave  components  of 
highest  frequency  will  be  attenuated  most,  with  resultant  distortion. 

The  KR  law  has  sometimes  been  applied  to  the  determination  of 
the  maximum  permissible  length  of  a  given  cable  for  efficient  trans- 
mission. Sir  William  Preece  has  stated  a  limit  of  15,000  for  the  value 
of  KR.  This  law  can  be  used  without  doubt  for  first  approximations, 
but  it  takes  no  account  of  wave  reflection  at  the  terminals  or  at  junc- 
tions of  dissimilar  portions  of  the  circuit.  Hence  it  should  be -used 
with  care  and  should  be  supplemented  by  more  elaborate  calculations 
in  the  actual  work  of  design. 

Open-wire  Lines.  —  In  addition  to  resistance  and  capacity,  lines 
of  open  wire  possess  inductance  and  leakage.  The  natural  inductance 
is  comparatively  small,  amounting  to  a  few  milli-henrys  per  mile. 
The  leakage  varies  greatly  with  weather  conditions;  the  insulation 
resistance  varies  from  perhaps  fifty  megohms  per  mile  in  clear  dry 
weather  to  a  fraction  of  a  megohm  per  mile  during  a  rainfall.  Theory 
and  experience  show  that  a  moderate  degree  of  leakage  improves  the 
quality  of  transmission,  that  is,  reduces  distortion.  But  extreme 
values  increase  the  attenuation  and  thus  reduce  the  total  efficiency. 

For  moderate  distances  of  a  few  hundred  miles  or  less,  No.  12 
N.  B.  S.  G.  wire  of  hard-drawn  copper  has  been  used  a  great  deal,  with 
satisfactory  results.  The  very  long  circuits  require  No.  8  B.  W.  G., 
which  is  about  two  and  one-half  times  the  weight  of  No.  12.  Other 
sizes  have  been  used  to  some  extent,  notably  No.  14  N.  B.  S.  G.,  for 
short  lines,  but  it  lacks  sufficient  tensile  strength.  Iron  has  been 
used  a  good  deal  in  rural  service  and  is  satisfactory  for  very  short 
lines,  but  extremely  inefficient  compared  with  copper,  because  of  its 
very  high  effective  resistance. 

The  efficiency  of  open-wire  lines  will  be  increased  in  general  by 
diminishing  the  resistance  and  the  capacity  and  increasing  the  in- 
ductance and  the  insulation  resistance.  When  a  metallic  circuit  of 
copper,  of  a  stated  size  of  wire,  is  erected  with  a  fixed  separation 
between  the  wires  the  inductance  and  the  capacity 'are  also  fixed. 
The  separation  ordinarily  employed  is  about  12  inches,  which  cannot 
well  be  increased  if  there  are  several  circuits  on  the  poles  or  cross- 
arms.  High  transmission  efficiency  is  therefore  obtained  by  diminish- 
ing the  resistance,  that  is,  by  using  larger  conductors. 


3i8  TOLL  TELEPHONE  PRACTICE 

Several  attempts  have  been  made  to  increase  the  natural  inductance, 
but  without  successful  results.  The  introduction  of  inductance  does 
not,  as  sometimes  stated,  neutralize  the  capacity  after  the  manner  so 
well  understood  in  simple  series  circuits.  Here  the  inductance  is 
serially  connected  with  the  circuit,  while  the  capacity  is  connected 
in  shunt,  and  the  frequency  varies  over  a  great  range.  The  effect  of 
inductance  is  to  increase  the  impedance  of  the  circuit  and  diminish 
the  current,  but  less  energy  is  frittered  away  as  heat  through  resist- 
ance losses  and  a  larger  percentage  of  outgoing  current  reaches  the 
distant  terminal,  when  inductance  is  present. 

The  advantages  of  large  inductance  were  early  pointed  out  by 
Oliver  Heaviside  and  in  1893  he  suggested  the  introduction  of  lumped 
artificial  inductance,  distributed  at  intervals  along  the  line.  This 
was  attempted  later  with  very  large  inductances  placed  many  miles 
apart,  but  the  effect  was  detrimental.  Nothing  was  accomplished 
until  Dr.  Michael  I.  Pupin  investigated  the  problem  mathematically 
and  experimentally  and  announced  the  results,  in  1900. 

Loaded  Lines.  —  The  underlying  theory  of  loaded  circuits  requires 
the  extended  use  of  mathematics  and  has  been  so  extensively  treated 
elsewhere  that  it  will  not  be  given  here.  Dr.  Pupin  thoroughly  ex- 
pounded the  subject  in  a  paper  read  before  the  American  Institute 
of  Electrical  Engineers,  in  1900.  In  explaining  the  benefits  of  in- 
ductance loading  he  made  use  of  a  mechanical  analogy  which  is  of 
great  assistance  in  grasping  the  subject.  Quotations  from  Dr.  Pupin 's 
paper  follow. 

"The  main  features  of  this  theory  are  extremely  simple  and  can 
be  explained  by  a  simple  mechanical  illustration.  Consider  the 
arrangement  in  Fig.  194.  A  tuning  fork  has  its  handle  C  rigidly 
fixed.  To  one  of  its  prongs  is  attached  a  flexible  inextensible  cord 
BD.  One  terminal  of  the  cord  is  fixed  at  D.  Let  the  fork  vibrate 
steadily,  the  vibrations  being  maintained  electromagnetically  or  other- 
wise* The  motion  of  the  cord  will  be  a  wave  motion.  If  the  fric- 
tional  resistances  opposing  the  motion  of  the  cord  are  negligibly  small 
the  wave  motion  will  be  approximately  that  of  stationary  waves  as 
at  2.  The  direct  waves  coming  from  the  tuning  fork  and  the  reflected 
waves  coming  from  the  fixed  point  D  will  have  nearly  equal  amplitude 
and  by  their  interference  form  approximately  stationary  waves. 

"  If,  however,  the  frictional  resistances  are  not  negligibly  small, 
then  there  will  be  dissipation  of  the  propagated  wave  energy.  Hence 


ELECTRICAL  REACTIONS  IN  TELEPHONE  LINES 


the  direct  and  the  reflected  waves  will  not  have  equal  amplitudes 
and,  therefore,  their  interference  will  not  result  in  stationary  waves. 
The  attenuation  of  the  wave  is  represented  graphically  at  3.  Experi- 
ments will  show  that,  other  things  being  equal,  increased  density  of 


234-5 


78910 


FIG.  194.  —  Mechanical  Analogy  of  a  Loaded  Circuit. 

the  string  will  diminish  attenuation,  because  a  larger  mass  requires  a 
smaller  velocity  in  order  to  store  up  a  given  quantity  of  kinetic  energy, 
and  smaller  velocity  brings  with  it  a  smaller  frictional  loss. .  This  is 
a  striking  mechanical  illustration  of  a  wave  conductor  of  high  induct- 


32O  |TOLL  TELEPHONE  PRACTICE 

ance.  It  should  be  observed  here  that  an  increase  of  the  density  will 
shorten  the  wave  length. 

"  Suppose  now  that  we  attach  a  weight,  say  a  ball  of  beeswax,  at 
the  middle  point  of  the  string,  in  order  to  increase  the  vibrating  mass. 
The  weight  will  become  a  source  of  reflection  and  less  wave  energy 
will  reach  the  point  D  than  before.  The  efficiency  of  transmission 
will  be  smaller  now  than  before  the  weight  was  attached.  Subdivide 
now  the  beeswax  into  three  equal  parts  and  place  them  at  three  equi- 
distant points  along  the  cord.  The  efficiency  of  wave  transmission 
will  be  better  now  than  it  was  when  all  the  wax  was  concentrated  at 
a  single  point.  By  subdividing  still  further  the  efficiency  will  be  still 
more  improved;  but  a  point  is  soon  reached  when  further  subdivision 
produces  an  inappreciable  improvement  only.  This  point  is  reached 
when  the  cord  thus  loaded  vibrates  very  nearly  like  a  uniform  cord 
of  the  same  mass,  tension,  and  frictional  resistance.  Such  a  loaded 
cord  with  a  tuning  fork  attachment  is  shown  at  4. 

"  If  an  increase  in  efficiency  of  wave  transmission  over  a  cord  thus 
loaded  is  to  be  obtained,  it  is  evident  that  the  load  must  be  properly 
subdivided  and  the  fractional  parts  of  the  total  load  must  be  placed 
at  proper  distances  apart  along  the  cord,  otherwise  the  detrimental 
effects  due  to  reflections  resulting  from  the  discontinuities  thus  intro- 
duced will  more  than  neutralize  the  beneficial  effects  derived  from  the 
increased  mass. 

"  The  problem  of  finding  the  proper  distance  at  which  the  loads 
should  be  placed  is  a  definite  mathematical  problem  of  Analytical 
Mechanics,  but  unfortunately  it  has  never  been  solved.  In  Fig.  194, 
diagram  5  represents  a  cord  carrying  loads  at  proper  distances  apart. 
Experiments  with  cords  of  this  kind  will  soon  convince  one  that  the 
distance  between  loads  should  be  considerably  smaller  than  one-half 
of  the  Vave  lengths  of  the  wave  which  is  to  be  transmitted.  So  that 
though  a  given  cord  may  be  properly  loaded  for  some  wave  lengths 
it  -will  not  be  properly  loaded  for  shorter  wave  lengths.  It  is  im- 
possible to  load  a  cord  in  such  a  way  as  to  make  it  equivalent  to  a 
uniform  cord  for  all  wave  lengths;  but  if  the  distribution  of  the  load 
satisfies  the  requirements  of  a  given  wave  length  it  will  also  satisfy 
them  for  all  longer  wave  lengths.  It  should  be  observed  now  that 
the  wave  length  which  is  considered  here  is  not  the  wave  length  of  the 
cord  without  the  loads,  but  the  wave  length  which  the  frequency 
under  consideration  will  have  on  the  properly  loaded  cord,  or,  what  is 


ELECTRICAL  REACTIONS  IN  TELEPHONE  LINES  321 

the  same  thing,  on  a  uniform  cord  of  the  same  mass,  tension,  and 
frictional  resistance,  as  the  loaded  cord.  This  point  is  of  fundamental 
importance,  for  the  wave  length  corresponding  to  a  given  frequency 
may  and  generally  will  be  much  shorter  on  the  loaded  cord  than  on 
the  cords  without  the  loads. 

"  A  cord  of  this  kind  is  a  mechanical  analogy  to  an  electrical  wave 
conductor.  The  mathematical  law  in  accordance  with  which  such 
a  cord  moves  is  the  same  as  that  in  accordance  with  which  the  elec- 
trical current  is  distributed  over  the  wave  conductor  under  the  action 
of  similar  forces.  The  reason  for  that  is  not  far  to  seek.  We  have- 
the  same  reactions,  viz.:  kinetic  or  mass  reaction,  tensional  reaction, 
and  the  resistance  reaction  in  the  case  of  the  cord.  Electro-kinetic 
reaction,  capacity  reaction,  and  ohmic  resistance  reaction  in  the  case 
of  the  wave  conductor.  The  mathematical  form  of  these  reactions 
is  the  same  in  both  cases,  hence  one  is  an  exact  analogy  of  the  other." 

It  will  be  noted  that  Dr.  Pupin  lays  considerable  stress  upon  the 
expression,  "  equivalence  between  a  non-uniform  conductor  and  its 
corresponding  uniform  conductor."  The  meaning  of  this  expression 
may  be  understood  more  readily  by  remembering  that  a  wave  of  a 
given  frequency  has  a  particular  wave  length  and  a  certain  amount 
of  attenuation.  Hence,  if  a  wave  of  a  given  frequency  has  the  same 
wave  length  and  attenuation  on  a  non-uniform  conductor  that  it 
has  on  a  uniform  conductor,  the  two  conductors  are  equivalent  to 
each  other. 

The  factors  which  enter  into  transmission  problems  are  numerous 
and  complicated.  Commencing  with  the  energy  of  sound  vibrations 
as  they  impinge  upon  the  diaphragm  of  the  transmitter,  and  passing 
through  all  the  steps  of  transformation  and  transmission,  to  the 
energy  emitted  by  the  receiver  diaphragm  at  the  distant  terminal, 
shows  most  forcibly  how  complex  the  problem  becomes  when  ade- 
quately treated.  Theoretical  considerations  are  indispensable  in 
practical  design,  but  considerable  data  of  an  empirical  nature  must 
necessarily  be  employed,  particularly  in  the  matter  of  transmission 
standards  and  the  efficiency  of  terminal  equipment. 

The  reduction  of  attenuation  in  loaded  lines  has  been  clearly  brought 
out  in  Dr.  Pupin's  paper,  before  referred  to;  the  following  is  a  quo- 
tation. 

1  To  bring  out  the  physical  meaning  of  the  attenuation  constant 
consider  two  consecutive  half  wave-lengths  at  any  moment.  The 


322  TOLL  TELEPHONE  PRACTICE 

one  nearest  to  the  transmitting  apparatus  shall  be  denoted  by  A  and 
the  other  by  B.  The  wave  energy  stored  up  in  the  medium  sur- 
rounding A  is  greater  than  that  stored  up  in  the  medium  surrounding 
B.  Hence  the  wave  energy  is  gradually  dissipated  during  its  propa- 
gation from  the  transmitting  to  the  receiving  apparatus,  and  there- 
fore the  amplitude  of  both  current  and  potential  becomes  smaller  as 
the  energy  progresses  along  the  transmission  line.  Let  U  be  the  am- 
plitude of  the  current  at  the  transmission  end,  and  Us  be  the  ampli- 
tude at  the  distance  s,  then  if  the  line  be  considered  infinitely  long 

§-s  =  ^5>    (9) 

where  e  is  the  base  of  Napierian  logarithms.  The  constant  0  is  called 
the  attenuation  constant.  The  mathematical  expression  for  0  is  well 
known. 

ft  =  \I-PC(V]W  +  R*  ~  PL),      ....     (10) 

where  L,  R}  C  are  the  inductance,  resistance,  and  capacity  respec- 
tively of  the  wave  conductor  per  unit  length  and  p  is  the  frequency 
speed." 

This  expression  for  0  shows  that  it  depends  upon  the  frequency, 
increasing  with  it.  Therefore  the  highest  notes  or  harmonics  are 
attenuated  most  and  this  impairs  the  quality  of  transmission,  or  pro- 
duces distortion.  The  effect  of  this  is  to  render  transmitted  speech 
less  intelligible.  Dr.  Pupin  has  shown  that  high  inductance  obviates 
this  difficulty;  for  if  the  inductance  is  large  in  comparison  with  the 
resistance,  the  expression  for  0  becomes 


Now  as  this  equation  is  independent  of  the  frequency,  all  the  fre- 
quencies will  be  attenuated  alike.  Thus  a  relatively  large  inductance 
not  only  tends  to  decrease  attenuation  but  also  eliminates  distortion. 
This  assumes,  however,  that  the  coils  themselves  offer  the  same  prop- 
erties at  all  frequencies,  which  is  not  fully  realized  in  practice. 

The  method  of  inserting  the  inductance  coils  in  the  lines  is  shown 
in  Fig.  195  in  which  the  condensers  shown  serve  merely  to  represent 
the  distributed  capacity  of  the  line. .  Each  coil  consists  of  two  wind- 
ings, one  for  each  limb  of  the  circuit,  wound  on  a  ring-shaped  or 


ELECTRICAL  REACTIONS  IN  TELEPHONE  LINES 


323 


toroidal  core  which  is  composed  of  fine  soft  iron  wire,  thoroughly 
insulated  so  as  to  reduce  eddy  currents  to  a  minimum. 


FIG.  195.  —  Method  of  Inserting  Pupin  Coils  in  Telephone  Line. 


The  greatest  benefits  from  loading  are  secured  with  cable  circuits, 
whose  normal  efficiency  is  low.  Loaded  cables  are  now  extensively 
used,  both  in  this  country  and  abroad.  The  loading  of  aerial  lines 
seemed  at  first  to  be  successful,  but  it  was  found  that  the  normal 
gains  could  not  be  maintained  at  times  of  minimum  insulation.  The 
early  loading  was  carried  out  with  coils  having  about  2.5  ohms  of 
true  resistance  and  0.25  henry  of  inductance,  spaced  i\  miles.  It 
was  found  later  that  the  spacing  could  be  increased  to  eight  miles 
without  any  sacrifice  of  efficiency. 

Maintenance  troubles  later  developed,  due  to  breakdowns  of  coil 
insulation  from  lightning.  This  was  overcome  by  the  use  of  special 
arresters.  The  loading  of  aerial  lines  was  abandoned  temporarily, 
until  a  new  and  more  efficient  insulator  was  developed.  This  is  a 


FIG.  196.  —  Sinusoidal  Wave. 

double -petticoat  porcelain  type,  somewhat  larger  than  and  about  four 
times  as  expensive  as  the  standard  pony  glass.  The  results  obtained 
with  it  are  quite  satisfactory  and  extensive  loading  of  aerial  lines  is 
now  under  way,  including  phantom  circuits. 

A  very  complete  discussion  of  the  practice  of  loading  was  given  by 
Mr.  Hammond  V.  Hayes,  in  a  paper  read  before  the  International 
Electrical  Congress  at  St.  Louis,  which  is  abstracted  in  what  follows. 


324  TOLL  TELEPHONE  PRACTICE 

In  every  problem  affecting  the  transmission  of  telephone  waves 
over  a  line  there  are  two  factors  to  be  considered,  the  attenuation 
and  the  distortion  of  the  waves.  The  loss  of  energy  of  the  waves  on 
the  line  must  be  kept  at  a  minimum;  and  the  several  component 
telephone  or  voice  waves  must  be  transmitted  with  equal  relative 
impairment.  The  introduction  of  lumped  inductance  in  the  form 
of  loading  coils  tends  to  increase  the  distortion  by  the  possible 
unequal  reflection,  at  the  coils,  of  the  component  waves  of  different 


FIG.  197.  —  Complex  Voice  Wave. 

frequencies,  and  by  the  possible  unequal  attenuation  of  the  several 
waves  in  passing  through  the  coils.  This  action  was  referred  to  by 
Dr.  Pupin  in  his  mechanical  analogy  of  wave  motion,  which  has 
already  been  discussed. 

The  mathematical  work  of  Doctors  Pupin  and  Campbell  shows  con- 
clusively that  if  several  loading  coils  lie  within  a  wave  length,  on  any 
particular  loaded  circuit,  and  the  coils  themselves  are  theoretically 
perfect,  the  circuit  is  distortionless.  The  spacing  of  the  coils  in  prac- 
tice, therefore,  depends  simply  upon  a  determination  of  the  highest 
frequency  that  materially  affects  the  quality  of  speech.  It  has  been 
found  convenient,  in  studying  the  spacing  of  loading  coils,  to  deter- 
mine the  number  of  coils  on  each  particular  circuit  that  will  be  passed 
•by  some  given  point  .of  a  wave  in  one  second.  As  the  velocity  of  all 
waves  on  a  given  circuit  is  nearly  the  same  and  as  the  wave  length 
at  a  given  frequency  can  be  determined  from  the  velocity,1  the  num- 
ber of  coils  lying  within  any  particular  wave  length  can  be  readily 
determined.  A  large  number  of  long  telephone  circuits  have  been 
equipped  with  loading  coils  and  very  carefully  tested.  The  spacing 
of  the  coils  is  such  as  to  produce  a  range  of  the  number  of  coils  per 

1  The  wave  length  is  equal  to  the  velocity  divided  by  the  frequency. 


ELECTRICAL   REACTIONS   IN  TELEPHONE  LINES  325 

second  between  13,000  and  7000.  A  comparison  of  the  transmission 
over  various  circuits  has  shown  that  the  quality  of  transmission  is 
not  appreciably  impaired,  even  with  the  lower  number  of  coils  per 
second.  As  this  would  materially  attenuate  the  waves  of  very  high 
frequency,  it  seems  to  indicate  the  lack  of  importance  of  the  overtones 
of  very  high  periodicity  in  the  successful  transmission  of  speech. 

It  can  be  said,  therefore,  with  great  certainty,  that  the  distortion 
due  to  line  reflection  losses  in  a  loaded  telephone  circuit  can  be  neg- 
lected, provided  that  the  coils  are  so  spaced  along  the  lin£  as  to  give 
at  least  7000  coils  per  second,  and  provided  that  this  spacing  is  sub- 
stantially uniform  throughout  the  line.  To  entirely  eliminate  dis- 
tortion in  a  loading  coil,  it  must  be  designed  so  that  the  effective 
resistance  or  impedance  of  the  coil  to  all  telephonic  frequencies  is  the 
same.  Such  a  coil  is  theoretical  and  cannot  be  obtained  in  practice. 

A  loading  coil  is  primarily  designed  to  provide  the  required  amount 
of  inductance,  and  must  of  necessity  consist  of  numerous  turns  of 
wire.  Moreover,  to  minimize  attenuation,  it  is  imperative  that  the 
resistance  of  the  coil  be  kept  as  low  as  possible.  To  make  the  resist- 
ance of  the  coil  low,  the  wire  employed  should  be  of  copper,  of  large 
size,  and  the  number  of  turns  of  wire  in  the  coil  should  be  kept  small. 
A  reduction  in  the  turns  can  be  most  easily  obtained  by  the  use  of 
iron  for  the  core.  If  the  coil  is  made  entirely  of  copper,  the  effective 
resistance  will  differ  from  the  ohmic  resistance  by  an  amount  corre- 
sponding to  the  loss  due  to  eddy  currents  in  the  copper.  If  iron  forms 
the  core  instead  of  air,  there  will  be,  in  addition  to  the  eddy-current 
losses  in  the  copper,  eddy-current  losses  and  hysteresis  losses  in  the 
iron,  which  will  augment  the  difference  between  the  ohmic  resistance 
and  the  effective  resistance.  As  it  is  impossible  to  eliminate  the 
eddy-current  and  hysteresis  losses  entirely,  the  effective  resistance 
of  a  loading  coil  will  vary  with  different  periodicities,  and  thereby 
produce  distortion  in  the  transmitted  telephone  waves.  The  differ- 
ence between  the  ohmic  resistance  and  the  effective  resistance  at 
telephonic  frequencies  can  be  made  much  smaller  in  a  coil  composed 
entirely  of  copper  than  in  one  having  an  iron  core.  But  practical 
and  commercial  reasons  demand  the  latter,  provided  that  such  a  coil 
can  be  so  designed  that  its  use  in  a  telephone  circuit  will  not  be  pro- 
ductive of  appreciable  distortion. 

To  determine  whether,  in  practice,  there  is  appreciably  more  dis- 
tortion introduced  by  loading  coils  having  iron  cores,  as  compared 


326  TOLL  TELEPHONE  PRACTICE 

with  those  made  entirely  of  copper,  two  circuits  were  equipped, 
one  with  iron-cored  coils  and  the  other  with  copper  coils.  The  cir- 
cuits were  each  about  1000  miles  in  length.  The  coils  had  the  same 
inductance  and,  approximately,  the  same  ohmic  resistance.  The 
impedance  of  the  coil  having  an  iron  core  was  about  15.5  ohms  at  a 
frequency  of  2000  per  second,  and  that  of  the  copper  coil  n.8  ohms 
at  the  same  frequency.  These  circuits  thus  loaded  were  compared 
with  the  greatest  care,  and  no  difference  was  apparent  either  in  the 
character  or  the  quality  of  the  telephone  transmission.  These  tests 
are  again  confirmatory  of  the  fact  that  suppression,  or  reduction,  of 
the  voice  waves  of  the  highest  frequencies  does  not  appreciably 
affect  the  quality  or  intelligibility  of  transmitted  speech.  This  ex- 
periment was  considered  as  demonstrating  conclusively  the  possibility 
of  the  commercial  use  of  loading  coils  having  cores  of  iron. 

A  discussion  of  the  theoretical  dimensions  of  loading  coils  for  the 
different  classes  of  circuits  may  be  found  in  Dr.  G.  A.  Campbell's 
paper  in  the  Philosophical  Magazine  for  March,  1903.  In  practice, 
the  size  and  cost  of  the  coils  are  factors  requiring  serious  consideration. 
For  aerial  circuits,  where  the  line  wire  is  large  and,  consequently, 
the  resistance  of  the  circuit  is  small,  it  is  of  the  utmost  importance 

TJ 

that  the  effective  time  constant  —  of  the  coil  should  be  made  as  large 

H 

as  consistent  with  reasonable  cost.  Except  in  so  far  as  the  cost  is 
affected,  the  size  of  the  aerial  loading  coil  is  of  no  special  moment, 
as  the  coils  may  be  mounted  singly  upon  the  poles.  The  time  con- 
stant of  a  coil  can  be  increased  by  enlarging  its  size,  but  this  increases 
the  cost.  Following  the  theoretical  considerations  as  deduced  by 
Dr.  Campbell,  the  resistance  of  the  coils  that  have  been  used  on 
aerial  circuits  has  been  made  2.4  ohms.  The  design  of  the  core,  the 
permeability  of  the  iron  and  the  subdivision  of  the  iron  and  copper 
have  been  made  such  that  a  loading  coil  has  been  produced  having 
an  inductance  of  0.25  henry,  a  time  constant  of  0.048  second  at  a 
frequency  of  1000,  and  a  bulk  of  approximately  314  cubic  inches. 
This  coil  is  toroidal  in  shape,  ten  inches  in  diameter  and  four  inches 
high.  It  has  an  effective  resistance  of  15.5  ohms  at  2000  periods  per 
second. 

Coils  designed  for  use  in  cable  circuits,  in  which  the  size  of  wire  is 
much  smaller,  do  not  need  to  be  made  of  as  low  resistance  as  the  coil 
above  described.  Consequently,  their  size  and  time  constant  may 


ELECTRICAL  REACTIONS   IN  TELEPHONE  LINES  327 

.be  made  much  smaller.  Large  numbers  of  loading  coils  have  been 
placed  m  service,  their  design  varying  with  the  character  of  the  circuit 
on  which  they  were  used. 

In  the  terminal  apparatus  at  present  used  in  telephony,  or  where 
there  is  a  condition  of  non-uniformity  hi  the  character  of  the  line, 
the  telephone  waves  suffer  reflection;  this,  in  many  cases,  is  effective 
hi  materially  increasing  the  attenuation.  The  reflection  is  particu- 
larly pronounced  at  the  point  where  an  unloaded  section  is  connected 
to  a  loaded  section.  The  amount  of  reflection  is  greater,  the  greater 
the  divergence  from  homogeneity.  Thus,  a  section  halving  a  large 
inductance  per  mile,  when  connected  with  a  non-loaded  section, 
exerts  a  larger  reflective  action  than  one  having  a  smaller  inductance 
per  mile.  In  practice,  the  effect  of  reflection  is  of  considerable  im- 
portance, particularly  when  the  loaded  section  is  relatively  short. 
Theoretically,  these  reflections  may  be  eliminated  by  the  use  of  a 
perfect  transformer  (repeating  coil)  introduced  at  every  point  of 
non-uniformity  in  the  line.  Even  if  such  a  perfect  transformer  could 
be  made,  its  introduction  on  commercial  circuits  is  open  to  practical 
objections  and,  as  a  substitute,  a  terminal  taper,  which  consists  of 
a  series  of  coils  of  varying  inductance,  has  been  employed.  The 
arrangement  of  the  several  coils  constituting  the  taper  is  such  that  a 
coil  having  an  inductance  somewhat  less  than  that  of  the  coils  used 
on  the  loaded  section  is  placed  nearest  the  loaded  portion  of  the  line, 
a  coil  of  inductance  somewhat  less  than  the  first  is  placed  next  in 
order  and  a  coil  of  still  smaller  inductance  is  placed  nearest  the  non- 
lolled  section,  or  the  terminal  apparatus.  The  spacing  of  coils  in 
the  taper  corresponds  with  that  of  the  coils  on  the  line  of  which  it  is 
to  form  the  terminal. 

The  following  figures,  as  given  by  Mr.  Hayes,  illustrate  the  results 
which  have  been  obtained  on  several  typical  commercial  circuits. 
In  what  follows,  all  comparisons  are  made  on  the  basis  of  relative 
attenuation  between  similar  circuits  loaded  and  unloaded,  without 
reference  in  any  way  to  distortion  or  quality  of  transmitted  speech. 
The  curves  shown  hi  these  figures  are  the  results  of  actual  tests,  made 
on  commercial  loaded  circuits,  using  standard  terminal  apparatus  at 
the  transmitting  and  receiving  stations. 

In  Fig.  198  are  shown  the  results  obtained  in  tests  of  heavily  loaded 
standard  telephone  cable.  In  this  cable  the  wires  are  0.03589  of  an 
inch  in  diameter,  having  a  resistance  of  about  96  ohms  per  mile  of 


328 


TOLL  TELEPHONE  PRACTICE 


metallic  circuit.  The  mutual  capacity  between  the  two  wires  of  the 
circuit  is  0.068  of  a  microfarad  per  mile.  The  inductance  added  to 
the  circuit  by  the  loading  coils  amounted  to  about  0.6  of  a  henry  per 
mile.  In  the  figure,  the  abscissae  represent  lengths  of  cable  and  the 


LENGTH  OP  CABLE 
FIG.  198.  —  Heavily  Loaded  Cable. 

ordinates  the  relative  strengths  of  current.  Curve  i  is  that  repre- 
senting the  attenuation  of  current  on  an  unloaded  circuit  as  the 
length  of  the  cable  is  increased. 

It  will  be  seen  that  the  attenuation  increases  very  rapidly  as  the 
length  of  the  cable  increases.  Curve  2  represents  the  attenuation  on  a 
similar  circuit,  but  loaded  as  above  described,  the  terminal  telephone 
being  placed  directly  at  the  ends  of  the  loaded  cable,  thereby  obtaining 
the  full  effects  of  reflection.  It  will  be  noticed  that  the  initial  current  on 
the  loaded  circuit  is  about  one-quarter  of  that  on  the  unloaded  circuit. 
Moreover,  the  transmission  on  shorter  lengths  of  the  loaded  circuit, 
under  these  conditions,  is  much  poorer  than  the  transmission  over 
similar  lengths  of  the  same  circuit  unloaded.  But  the  rate  of  atten- 
uation per  unit  of  distance  is  much  less  on  the  loaded  than  on  the 
unloaded  circuit;  so  that  for  the  longer  lengths  of  circuit,  the  transmis- 


ELECTRICAL   REACTIONS  IN  TELEPHONE   LINES 


329 


sion  is  superior  on  the  loaded  circuit  to  that  on  the  same  lengths 
unloaded.  Curve  3  shows  the  attenuation  where  terminal  tapers  are 
employed  at  the  two  ends  of  the  loaded  circuit  and  the  telephone 
transmitting  and  receiving  apparatus  is  connected  directly  to  the 
tapers.  Here,  again,  the  initial  current  is  considerably  less  than  that 
on  the  unloaded  circuit  and  the  transmission  on  short  lengths  of  cir- 
cuit is  better  on  the  unloaded  than  on  the  loaded  conductors.  But 
the  introduction  of  the  tapers  on  the  loaded  circuit  has  more  than 


80  100 

CABLE 


FIG.  199.  —  Cable  With  Medium  Loading. 

doubled  the  initial  current  and  has  shortened  the  equivalent  length 
of  the  circuit  by  more  than  one-half.  A  comparison  of  curves  2  and  3 
shows  how  great  a  factor  reflection  losses  are  between  the  terminal 
apparatus  and  the  line  and  the  importance  of  the  taper  in  reducing 
these  losses.  In  practice  it  has  been  found  that  reflection  losses  can 
be  still  further  reduced  and,  under  special  conditions,  almost  entirely 
eliminated. 

In  the  case  above  described,  a  large  amount  of  inductance  has  been 
added  to  the  circuit.  The  results  which  have  been  obtained  upon 
cables  where  less  inductance  has  been  added  are  shown  in  Fig.  199. 


330 


TOLL  TELEPHONE  PRACTICE 


In  this  case  the  cable  is  substantially  similar  to  that  previously  de- 
scribed. Upon  it  loading  coils  are  placed  so  as  to  bring  the  inductance 
of  the  circuit  down  to  approximately  0.17  of  a  henry  per  mile.  In 
other  words,  the  inductance  is  less  than  one-third  of  that  in  the  case 
just  described.  In  Fig.  199  curve  i  is  similar  to  that  in  Fig.  198,  and 
represents  the  attenuation  of  the  telephone  current  in  an  unloaded 
circuit.  Curve  2  represents  the  attenuation  in  the  lightly  loaded 
circuit  when  no  tapers  are  employed  and  the  telephone  transmitting 


400  600  800  1000 

LENGTH  OF  LINE: 


1600 


FIG.  200.  —  Loaded  Circuit"  of  No.  8  B.W.G.  Copper  Open  Wire. 

and  receiving  apparatus  is  placed  at  the  terminals  of  the  cable.  It 
will  be  noted  that  the  reflection  losses  are  much  less  in  the  case  of  the 
lightly  loaded  cable  than  in  the  previous  case.  In  fact,  in  the  shorter 
lengths  of  cable  the  lighter  loading  is  more  effective  than  the  heavier. 
For  the  longer  lengths,  however,  the  heavier  loading  gives  better 
results.  With  proper  apparatus  at  the  terminals  of  the  loaded  cable 
to  reduce  reflection  losses,  much  less  attenuation  would  result  than 
is  indicated  by  curve  2. 

In  Fig.  200  are  shown  the  results  which  have  been  obtained  on 
open-wire  circuits,  composed  of  copper  weighing  435  pounds  to  the 


ELECTRICAL  REACTIONS  IN  TELEPHONE  LINES 


331 


mile.  On  these  circuits  loading  coils  were  so  placed  as  to  give  an  in- 
ductance of  about  o.  i  of  a  henry  per  mile.  Curve  i  shows  the  attenua- 
tion, with  various  lengths  of  line,  upon  a  similar  unloaded  circuit; 
and  curve  2  shows  the  attenuation  on  the  loaded  circuit  when  the 
telephone  transmitting  and  receiving  apparatus  is  placed  directly  at 
the  end  of  the  line  without  tapers.  Curve  3  shows  the  attenuation 
under  similar  conditions  when  tapers  are  employed.  The  results 
resemble  those  obtained  with  loaded  and  unloaded  cables.  There  is 


ZOO         400         €00         £00         1000 

LENGTH  or  LINE: 


MOO        I60O 


FIG.  201.  —  Loaded  Circuit  of  No.  12  N.  B.  S.  G.  Copper  Open  Wire. 

a  large  reflection  loss  which  is  considerably  reduced  when  tapers  are 
employed.  Even  with  tapers  the  loaded  line  for  shorter  distances  is 
inferior  to  the  unloaded. 

Fig.  201  illustrates  the  results  which  have  been  obtained  from 
loading  open- wire  circuits,  using  a  conductor  weigMng  173  pounds 
per  mile  and  having  an  added  inductance  equal  to  about  o.i  of  a 
henry  per  mile.  As  before,  curve  i  represents  the  attenuation  on  a 
similar  unloaded  circuit;  curve  2,  the  loaded  circuit  without  tapers; 
and  curve  3,  the  loaded  circuit  with  tapers. 

The  following  are  Mr.  Hayes'  general  conclusions.     The  curves 


332  TOLL  TELEPHONE  PRACTICE 

show  the  results  which  have  been  obtained  by  the  use  of  considerable 
inductance  added  to  open-wire  and  cable  telephone  circuits,  and  may 
be  considered  as  typical  of  the  results  obtained  on  similar  circuits  of 
different  capacity  or  composed  of  wires  of  different  size.  -  As  before 
stated,  the  curves  illustrate  simply  the  relative  volume  of  trans- 
mission under  the  various  conditions  described.  In  the  case  of  cables, 
there  is  a  distinct  improvement  in  the  quality  of  transmission  produced 
by  the  introduction  of  load  coils,  that  is,  a  reduction  in  distortion  and 
again  in  intelligibility.  The  high  insulation  that  can  be  maintained 
at  all  times  on  cable  circuits  renders  it  possible  to  introduce  loading 
coils  without  danger  of  materially  augmenting  leakage  losses.  The 
marked  diminution  in  attenuation,  the  improvement  in  quality  of 
transmission,  and  the  ease  with  which  inductance  coils  can  be  placed 
on  cable  circuits  without  introducing  other  injurious  factors,  such 
as  leakage  or  cross  talk,  render  the  use  of  loaded  cable  conductors 
especially  attractive.  The  reduction  of  attenuation  that  can  be 
obtained  by  the  use  of  load  coils  on  aerial  circuits,  even  under  theo- 
retically perfect  conditions,  is  less  than  can  be  obtained  on  cable 
circuits.  The  difference  in  the  effectiveness  of  loading,  between  the 
two  classes  of  circuits,  so  far  as  attenuation  is  concerned,  can  be 
explained  by  the  fact  that  in  a  cable  circuit  the  capacity  is  large  and 
the  inductance  of  the  circuit  itself  is  practically  negligible,  due  to  the 
close  proximity  of  the  two  conductors  forming  the  circuit.  In  aerial 
circuits,  on  the  other  hand,  the  distance  between  the  two  conductors 
is  such  as  to  make  the  capacity  of  the  circuit  much  less  and  its  induc- 
tance much  greater.  The  larger  self -inductance  of  the  open- wire 
circuit  operates  to  decrease  the  attenuation  and  decreases  the  relative 
usefulness  of  the  load  coils.  The  insulation  of  an  aerial  circuit  cannot 
be  maintained  either  as  high  or  constant  as  that  of  a  cable,  and  the 
introduction  of  loading  coils  tends  to  increase  the  losses  due  to  leak- 
age. Moreover,  there  is  not  the  same  improvement  in  the  quality  of 
transmission  on  a  loaded  aerial  circuit,  as  compared  with  a  similar 
unloaded  circuit,  as  there  is  between  loaded  and  unloaded  cables.  Ini- 
tially, open- wire*  circuits  are  largely  free  from  distortion;  whereas  the 
distortion  on  long  cable  circuits  is  considerable.  The  addition  of 
load  coils  to  aerial  circuits  cannot  be  expected,  therefore,  to  effect 
much  improvement  in  the  quality  of  transmission. 

The  recent  developments  in  loading  underground  toll  cables  are 
especially  noteworthy  as  marking  a  distinct  advance  in  the  art.     The 


ELECTRICAL  REACTIONS  IN  TELEPHONE  LINES  333 

first  long  cable  of  this  character  was  installed  between  New  York  and 
Philadelphia,  a  distance  of  90  miles.  It  consists  of  112  pairs  of  No.  14 
B.  &  S.  copper  conductors,  with  dry  paper  insulation.  The  resist- 
ance is  13.7  ohms  and  the  mutual  capacity  is  0.065  microfarad  per 
mile.  The  loading  coils  are  spaced  1.25  miles  apart  and  have  an 
inductance  of  0.25  henry.  The  commercial  efficiency  of  transmission 
has  been  termed  by  Mr.  J.  J.  Carty  a  "  fourteen  mile  talk."  The 
general  standard  of  comparison  is  one  mile  of  No.  19  B.  &  S.  standard 
(or  low-capacity)  cable.  The  85-mile  cable  between  Chicago  and 
Milwaukee  is  composed  of  120  pairs,  of  which  60  are  No.  14  B.  &  S. 
and  60  No.  16  B.  &  S.  In  every  case  these  cables  have  dry  paper 
insulation  and  are  very  carefully  balanced  to  avoid  cross  talk. 


CHAPTER  XIX 
CROSS   TALK  AND   INDUCTIVE   DISTURBANCES 

THE  effects  of  distributed  resistance,  inductance,  capacity  and 
leakage  upon  the  transmission  of  energy  in  a  telephone  line  were 
shown  in  the  preceding  chapter.  It  was  there  assumed,  however, 
that  the  line  had  no  inductive  relations  with  other  lines,  or  in  other 
words,  that  no  parallel  lines  existed  anywhere  in  its  neighborhood. 
Such  isolation  is  very  infrequent  in  practice  and  inductive  relation- 
ships must  ordinarily  be  taken  into  account.  In  general  these  rela- 
tionships are  of  two  kinds:  first,  those  which  exist  between  two  or 
more  parallel  telephone  lines;  and  second  those  which  exist  between 
a  telephone  line  and  some  line  of  different  character,  as  for  example 
a  power  transmission  line,  or  a  railway  feeder. 

Induction  of  the  first  kind  is  generally  termed  cross  talk,  because 
it  destroys  the  secrecy  of  communication  and  results  in  overhearing 
messages  or  conversations  in  neighboring  lines.  That  of  the  second 
kind  is  generally  known  by  the  broad  term  induction,  which  implies 
any  kind  of  foreign  disturbance.  Both  kinds  are  objectionable  and 
injurious  to  service,  and  their  prevention  or  elimination  forms  an 
important  branch  of  telephony.  Cross  talk  can  only  manifest  itself 
in  a  single  form,  but  induction  takes  many  forms.  The  latter,  for 
example,  is  often  a  steady  hum  or  tone  of  constant  fundamental 
pitch,  caused  by  exposure  to  parallel  lines  carrying  alternating  current 
at  25  or  60  cycles;  or  it  may  have  a  variable  pitch  and  intensity, 
corresponding  to  the  commutation  of  electric  railway  motors,  in  the 
case  of  exposure  to  trolley  or  feeder  circuits ;  or  again  it  may  be  harsh 
and  uneven,  caused  by  exposure  to  telegraph  circuits  operating  with 
some  form  of  morse  transmission. 

But  so-called  induction  is  not  always  caused  in  the  manner  its 
name  implies;  it  is  sometimes  conductive,  due  to  imperfect  insulation 
and  attendant  leakage.  There  is  no  leakage,  of  course,  between 
insulated  metallic  circuits  on  different  pole  lines,  but  only  between 
lines  on  the  same  poles.  In  the  case  of  grounded  lines,  or  metallic 
lines  carrying  normal  grounds,  differences  in  earth  potentials  may 

334 


CROSS  TALK  AND   INDUCTIVE  DISTURBANCES  335 

cause  foreign  currents  of  a  conductive  nature.  Such  potential  differ- 
ences are  caused  in  general  by  the  track  return  circuits  of  electric 
railways,  with  their  differences  of  potential  between  different  points 
when  cars  are  in  operation.  It  is  characteristic  of  such  potentials 
to  fluctuate  from  moment  to  moment,  corresponding  to  variations 
in  the  demands  for  power. 

In  the  very  early  stages  of  telephone  development,  the  grounded 
line  was  employed  exclusively.  But  its  limitations  soon  appeared; 
it  was  subject  to  severe  inductive  disturbances  which  it  seemed  hope- 
less to  prevent.  Parallel  lines  of  this  type  are  subject  both  to  exces- 
sive cross  talk  and  severe  foreign  disturbances.  The  latter  appeared 
in  a  prominent  degree  with  the  introduction  of  electric  traction, 
caused  by  the  commutation  of  the  motors.  Each  car  as  it  started 
caused  a  disturbance,  commencing  with  a  note  or  tone  of  very  low 
pitch,  rising  as  the  car  gathered  speed  and  becoming  very  shrill. 
The  fluctuations  of  earth  potentials  added  to  the  difficulties.  These 
conditions  practically  forced  the  adoption  of  the  metallic  form  of 
circuit,  which  is  not  only  subject  to  less  severe  induction  initially, 
but  can  also  be  transposed  to  reduce  or  eliminate  it.  Grounded  lines 
are  still  employed  extensively  in  rural  service,  but  the  extensions  of 
interurban  electric  railroads  and  high-tension  power  transmission  are 
making  it  more  difficult  to  maintain  them.  In  all  toll  systems  of 
any  size  or  importance,  metallic  circuits  are  imperative  to  good 
service. 

Induction  is  theoretically  of  two  kinds,  electromagnetic  and  electro- 
static; neither  kind  ever  exists  wholly  independent  of  the  other,  but 
one  kind  may  predominate.  The  first  kind  is  the  easier  to  under- 
stand in  a  physical  sense,  because  it  is  merely  a  form  of  transformer 
action,  in  which  the  foreign  or  disturbing  line  is  the  primary  and  the 
telephone  line  the  secondary.  The  first  sets  up  a  magnetic  field, 
which  is  the  inseparable  accompaniment  of  every  electric  current, 
and  some  portion  of  this  field  links  itself  with  the  telephone  line. 
Then,  as  the  primary  field  changes  in  direct  proportion  with  the 
primary  current,  from  instant  to  instant,  some  of  the  lines  of  the  field 
cut  the  telephone  conductors  and  induce  an  E.M.F.  therein.  The 
general  laws  of  electromagnetic  induction  apply  to  this  case,  of  course, 
but  as  compared  with  an  ordinary  transformer  the  transfer  of  energy 
from  primary  to  secondary  is  exceedingly  inefficient.  At  the  same 
time  the  secondary  action  may  be  large  in  a  telephonic  sense,  and 


336 


TOLL  TELEPHONE  PRACTICE 


Field  Surrounding  a  Single  Isolated 
Conductor. 


quite  possibly  so  severe  as  to  interfere  with  service  or  even  prevent  it 
entirely. 

The  character  of  the  magnetic  field  surrounding  a  single  conductor, 
whose  return  lies  at  a  considerable  distance,  is  illustrated  by  Fig.  202. 

The  lines  are  most  dense  at  the  sur- 
face of  the  conductor,  and  the  density 
diminishes  very  rapidly  with  increasing 
distances  from  the  conductor.  At  any 
given  point  the  field  intensity  is  pro- 
portional to  the  current,  and  changes 
instantaneously  as  the  current  changes, 
assuming  that  the  field  lies  in  a  dielec- 
tric medium  such  as  air.  The  flux 
lines  are  concentric  circles  about  the 
conductor  so  long  as  the  return  is  very 

FIG.  202.  —  Character  of  Magnetic    distant,  but  they  change  position  as 

the  return  is  brought  nearer,  and  in 
some  cases  change  in  shape.  Mag- 
netic flux  lines  are  in  longitudinal  tension  and  thus  tend  always  to 
shorten;  it  follows  that  transversely  they  are  in  compression. 

The  electric  field  is  less  readily  understood,  but  in  fact  almost  as 
simple  in  its  nature.  Just  as  currents  set  up  magnetic  forces  and 
fields  of  flux,  so  electric  potentials  set  up  electric  forces  and  corre- 
sponding fields  of  flux.  But  in  general,  electric  fields  are  everywhere 
in  the  dielectric  at  right  angles  with  the  magnetic  fields,  both  of  which 
spring  from  the  same  circuit.  Wherever  differences  of  electric  poten- 
tial exist,  there  is  an  electric  field  and  a  charged  dielectric.  A  poten- 
tial difference  implies  that  relatively  one  point  or  terminus  is  positive 
and  the  other  negative;  the  point  of  highest  potential  is  always  posi- 
tive, that  is,  it  tends  to  send  a  current  toward  the  point  of  lower 
potential.  At  the  same  time,  in  an  absolute  sense,  both  points  may 
be  positive,  or  both  negative. 

The  flux  lines  issue  from  the  positive  terminal  and  end  on  the 
negative  terminal,  so  that  a  free  positive  charge  would  be  impelled 
from  the  positive  to  the  negative  pole.  These  lines  are  in  tension 
and  thus  oppositely  charged  points  attract  each  other;  conversely, 
like  charges  repel  each  other.  While  a  magnetic  flux  line  is  always 
closed  on  itself,  an  electric  flux  line  has  two  free  ends,  one  of  which, 
however,  must  terminate  on  the  positive  point  or  pole  and  the  other 
on  the  negative  pole. 


CROSS  TALK  AND  INDUCTIVE  DISTURBANCES  337 

Fig.  203  illustrates  the  field  of  electric  flux  between  two  parallel 
plates,  oppositely  charged,  as  in  a  simple  elementary  condenser.     It 
is  a  well-known  fact  that  such  a  condenser  stores  a  definite  quantity 
of  electricity,  and  this  storage,  termed  an 
electric  charge,  accompanies  every  poten- 
tial difference  and  its  inseparable  electric 
field.     The  storage  actually  takes  place 
in  the  dielectric  which  composes  the  field 


and  is  sometimes  spoken  of  as  electric 

displacement.     The  displacement  can  be  FlG-2°3.— Lines  of  Electric  Force 

.       ...     ,,        ,   n     ,.  e  ^      e  and  Flux  Between  Two  Oppo- 

compared  with  the  deflection  of  the  free      sitdy  Charged  Plates 
end  of  a  beam  when  a  load  is  applied. 

In  reality,  an  electric  charge  represents  the  unbalanced  condition  of 
the  dielectric  under  potential  stress,  where  the  deflection  or  charge  is 
proportional  to  the  force  applied.  The  charge  is  also  proportional 
to  the  volume  of  dielectric  placed  under  stress,  assuming  a  simple 
arrangement  like  that  in  Fig.  203,  with  plates  separated  by  a  fixed 
distance. 

The  electric  stress  or  potential  in  the  dielectric  falls  from  the  posi- 
tive value,  at  the  surface  of  the  positive  plate,  to  the  negative  value 
at  the  opposite  plate,  in  a  gradual  manner.  This  potential  gradient 
varies,  however,  with  the  form  of  the  plates  or  terminals  and  their 
separation. 

It  will  now  be  evident  that  any  two  points  taken  at  random  in  the 
charged  field  may  be  at  different  points  on  the  potential  gradient. 
If  these  points  are  imagined  to  be  the  terminals  of  a  second  condenser, 
they  are  obviously  charged  by  induction.  Thus  if  a  metallic  body 
were  inserted  in  the  field,  there  would  be  an  exchange  of  charges,  by 
means  of  momentary  currents,  between  its  several  parts,  in  obedi- 
ence to  the  potential  differences  in  the  dielectric  which  it  replaced. 
This  is  illustrated  by  Fig.  204,  which  shows  a  charged  sphere  A  and 
a  cylinder  B  charged  by  induction.  The  electric  displacement  in  the 
cylinder  corresponds  to  the  displacement  in  the  dielectric  and  a  posi- 
tive charge  passes  from  X  to  F,  leaving  X  negatively  and  Y  posi- 
tively charged. 

If  the  impressed  electric  force  is  alternating,  the  displacements  or 
charges  alternate  likewise,  and  in  effect  an  alternating  current  flows 
through  the  dielectric,  or  the  condenser.  At  the  same  time  any 
conducting  bodies  within  the  field  will  circulate  local  alternating 


338  TOLL  TELEPHONE  PRACTICE 

currents,  caused  by  the  alternating  potential  gradient  which  they 
intercept.  For  example,  if  the  sphere  A  in  Fig.  204  is  charged  from 
an  alternating  source,  local  alternating  currents  will  circulate  in  the 
cylinder  B,  between  X  and  Y. 


FIG.  204.  —  Induced  Electric  Charges. 


The  nature  of  electrostatic  induction  in  the  case  of  two  parallel 
grounded  wires  is  shown  by  Fig.  205.  The  induced  charge  on  the 
telephone  line  is  proportional  at  every  instant  to  the  impressed  poten- 
tial on  the  disturbing  wire,  and  if  the  latter  is  alternating  there  will 
be  induced  alternating  currents  in  the  telephone  line.  When  the 
potential  of  the  disturbing  wire  is  constant  throughout  its  length  at 


DISTURBING   WIRE 


r  n 


FIG.  205.  —  Electrostatic  Induction  Between  Parallel  Wires. 

any  instant,  there  will  be  no  current  at  the  center  of  the  telephone 
line,  because  here  the  induced  charge  divides  and  half  flows  to  earth 
through  each  terminal. 

When  electromagnetic  and  electrostatic  induction  occur  simul- 
taneously, as  they  do  in  nearly  all  cases,  the  induced  current  and 
E.M.F.  are  the  resultants  of  both  kinds  of  induction.  The  electro- 
magnetic effect  is  an  induced  E.M.F.  in  the  telephone  line,  which 
gives  rise  to  a  flow  of  current  when  the  circuit  is  closed;  and  at  any 
instant  the  whole  flow  is  in  the  same  direction,  thus  differing  from 
the  case  of  pure  static  induction. 

When  the  disturbing  circuit  is  energized  by  a  purely  sinusoidal 
alternating  current  and  E.M.F.,  the  induced  current  and  E.M.F.  will 


CROSS  TALK  AND  INDUCTIVE  DISTURBANCES  339 

be  sinusoidal  likewise  and  of  the  same  frequency.  When  the  inducing 
or  primary  current  is  a  complex  wave  representing  transmitted  speech, 
however,  a  counterpart  of  these  currents  will  appear  in  the  secondary 
or  telephone  line,  and  will  reproduce  the  original  voice  sounds,  which 
is  simply  cross  talk. 

The  problem  of  eliminating  or  preventing  cross  talk  is  a  most  im- 
portant one  for  the  telephone  engineer,  not  only  as  it  concerns  the 
outside  plant,  but  switchboards,  apparatus  and  office  wiring  and 
cables.  In  devising  methods  to  prevent  it,  there  was  considerable 
speculation  as  to  whether  electrostatic  or  electromagnetic  effects 
predominated.  The  experiments  carried  out  by  Mr.  John  J.  Carty1 
in  this  connection  are  especially  interesting.  He  concluded  that  the 
electrostatic  effect  predominates  almost  completely  for  telephone  cir- 
cuits in  general. 

A  mathematical  analysis  of  the  case  by  Mr.  Louis  Cohen,  given  in 
another  paper  before  the  American  Institute  of  Electrical  Engineers, 


FIG.  206.  —  Carty's  F,xperiinental  Circuit  for  Demonstrating  Electrostatic  Induction. 

in  June,  1907,  shows  that  for  short  lines  the  electromagnetic  effect 
greatly  predominates,  but  becomes  relatively  less  for  longer  lines  and 
for  very  long  lines  is  entirely  overpowered  by  the  electrostatic  effect. 
He  also  points  out  that  under  the  conditions  of  Mr.  Carty's  experi- 
ments, the  electrostatic  effect  necessarily  predominated,  on  account 
of  the  alteration  of  the  line  characteristics  produced  by  the  intro- 
duction of  telephone  receivers. 

Fig.  206  shows  the  arrangements  in  one  of  Mr.  Carty's  experiments. 
AB  is  the  disturbing  wire,  which  contains  the  secondary  of  an  induc- 
tion coil ;  a  vibrating  tuning  fork  in  front  of  the  transmitter  was  used 
to  set  up  the  disturbing  E.M.F.  in  the  line.  The  receiver  Y  is  at 

1  See  the  Transactions  of  the  American  Institute  of  Electrical  Engineers,  1891,  Vol. 
VTII,  p.  114. 


340  TOLL  TELEPHONE  PRACTICE 

the  center  of  the  line,  X  at  one  end  and  Z  at  the  other.  These  lines 
were  about  200  feet  in  length  and  parallel  at  a  distance  of  one-eighth 
of  an  inch.  The  induced  charges  on  CD  have  an  outlet  to  ground 
through  the  terminal  receivers.  It  was  found  that  the  receiver  F 
was  silent,  while  X  and  Z  responded,  proving  the  electrostatic  nature 
of  the  induction;  this  result  could  not  have  been  obtained  if  electro- 
magnetic induction  were  present,  because  in  that  case  a  current  would 
flow  around  the  circuit  CD  as  a  whole  and  in  one  direction  only  at 
any  given  instant.  In  the  case  considered,  the  charges  divide  at  F 
and  flow  in  opposite  directions,  which  was  proven  by  opening  the 
line  at  that  point,  without  affecting  the  disturbances  in  the  receivers 
at  X  and  Z. 

No  electromagnetic  effect  could  be  observed  even  when  the  line 
AB  was  grounded  at  A,  so  as  to  produce  a  large  flow  of  primary 
current.  These  observations  were  further  confirmed  by  short-cir- 
cuiting one  of  the  receivers  in  CD,  as  shown  in  Fig.  207.  By  closing 


FIG.  207.  —  Carty's  Experimental  Circuit  for  Demonstrating  Electrostatic  Induction. 

the  key  at  C  one  end  of  the  line  was  directly  grounded,  and  in  that 
case  no  disturbance  was  observed  at  Z,  because  the  whole  induced 
charge  passed  over  the  low-resistance  line  and  through  C  to  ground. 
This  demonstrated  again  the  electrostatic  nature  of  the  induction 
and  the  absence  of  electromagnetic  effect. 

In  considering  the  feasible  or  possible  methods  of  preventing  induc- 
tion, the  most  obvious  simple  plan  is  that  illustrated  in  Fig.  208, 
where  the  telephone  wires  are  placed  equidistant  from  the  disturbing 
wire,  and  hence  at  equal  points  on  the  electrostatic  potential  gradient 
and  also  at  points  of  equal  field  strength  magnetically.  That  is, 
CD  is  as  far  from  AB  as  EF,  and  a  reference  to  Fig.  202  will  show 
that  each  is  linked  with  the  same  magnetic  flux  set  up  by  the  current 


CROSS  TALK  AND   INDUCTIVE  DISTURBANCES 


341 


in  AB.  It  is  important  to  observe,  however,  that  the  immunity  from 
disturbance  is  absolutely  dependent  on  the  perfect  balance  of  the 
telephone  circuit,  in  every  respect.  But  this  means  of  preventing 
induction  has  only  a  limited  application. 


+     + 


FIG.  208.  —  Arrangement  of  Disturbing  Wire  and  Metallic  Circuit  for 
Preventing  Induction. 

The  conditions  often  met  are  shown  in  Fig.  209,  where  the  disturb- 
ing wire  lies  wholly  on  one  side  of  the  telephone  line.  The  wire  CD, 
being  nearer  AB  than  EF,  is  at  a  higher  induced  potential  electro- 
statically than  EF,  and  at  the  same  time  has  induced  in  it  a  larger 
electromagnetic  E.M.F.  If  the  current  in  AB,  the  disturbing  wire, 
is  in  the  direction  shown  by  the  arrows  in  the  figure,  the  secondary 


r 


FIG.  209.  —  Unbalanced  Exposure  and  Resulting  Induction. 

electromagnetic  currents  will  flow  instantaneously  in  the  direction 
shown  by  the  heavy  arrows  and  the  static  currents  as  shown  by  the 
light  arrows. 

Evidently  the  average  distance  between  the  telephone  wires  and 
the  disturbing  wire  can  be  equalized  by  a  transposition  of  the  former 
at  the  center  of  exposure,  as  illustrated  in  Fig.  210.  This  will  com- 
pletely balance  the  electromagnetic  induction  and  eliminate  all  dis- 
turbances at  the  terminals  due  to  that  cause.  But  the  same  result 
will  not  be  obtained  with  reference  to  electrostatic  induction;  there 
the  effect  is  shown  by  Fig.  211.  The  major  portions  of  the  induced 


342 


TOLL  TELEPHONE  PRACTICE 


charges  will  neutralize  themselves  through  the  transposition,  but  a 
small  portion  in  each  case  flows  through  the  terminals.  There  will 
be  four  neutral  points  at  which  the. charges  divide  and  flow  in  opposite 
directions,  shown  at  W,  X,  Y  and  Z  in  the  figure.  These  points 
are  much  nearer  the  terminals  than  the  transposition. 


FIG.  210.  —  Effect  of  Single  Transposition  on  Electromagnetic  Induction. 

A  single  transposition  will  not  entirely  eliminate  the  electromagnetic 
effect  if  the  section  is  comparatively  long,  because  of  the  attenuation 
of  the  current.  Practical  results  are  secured  by  diminishing  the  sec- 
tion to  a  fraction  of  a  mile;  in  this  way  the  neutral  points  are  made 
to  approach  the  ends  of  the  section  so  closely  that  the  resulting  dis- 
turbance in  the  terminal  receivers  is  negligible,  or  inaudible.  t  Half- 

+  +  +  ++  +  +.+  + 


_ 

cflZ  C- 


FIG.  211.  —  Effect  of  Single  Transposition  on  Electrostatic  Induction. 

mile  or  quarter-mile  sections  are  sufficient  to  prevent  cross  talk  with 
"the  volume  of  transmission  which  occurs  in  ordinary  practice. 

In  the  discussion  of  inductive  disturbances  thus  far,  a  disturbing 
circuit  consisting  of  only  one  wire  has  been  considered,  since  this 
simplifies  in  a  measure  the  explanation  of  the  reactions.  In  the  study 
of  the  transposition  of  telephone  circuits  as  regards  one  another, 
however,  it  is  necessary  to  deal  with  two  wires  for  each  circuit;  and 
in  this  case,  when  the  transposition  of  numerous  circuits  is  contem- 
plated, the  problem  becomes  rather  complicated  and  requires  consid- 


CROSS  TALK   AND  INDUCTIVE  DISTURBANCES  343 

erable  study.  The  transposition  of  a  two-wire  metallic  circuit  consists, 
as  previously  indicated,  of  interchanging  the  relative  positions  of 
the  two  wires,  or  rotating  the  plane  of  the  circuit  through  180  de- 
grees. Then  if  only  two  telephone  circuits  are  considered,  which 
are  relatively  short,  a  transposition  of  one  of  them  at  its  middle  point 
will  serve  to  eliminate  cross  talk  between  the  two  circuits.  It  will 
also  prevent  foreign  circuits  from  affecting  the  transposed  circuit,  but 
not  the  other.  These  exterior  disturbances  may*  arise  from  a  power 
circuit  or  from  other  telephone  circuits,  and  when  more*  than  two 
circuits  are  considered,  all  but  one  will  have  to  be  transposed.  Also 
each  individual  circuit  must  be  transposed  with  reference  to  each  of 
the  other  circuits;  it  will  not  be  sufficient  to  transpose  them  all  in 
the  same  manner.  The  reason  for  this  will  be  appreciated  by  re- 
ferring to  Fig.  212,  in  which  is  shown  a  power  circuit  A,  paralleled  by 


FIG.  212.  —  Example  of  Improper  Transpositions. 

three  telephone  circuits  B,  C  and  D.  The  telephone  circuit  B  is  not 
transposed,  while  the  telephone  circuits  C  and  D  are  each  transposed 
at  their  middle  points.  Then  if  the  lines  are  relatively  short,  circuits 
C  and  D  will  be  free  from  the  inductive  disturbance  of  the  power 
circuit,  while  circuit  B,  which  is  not  transposed,  will  not.  Regarding 
the  inductive  action  between  the  telephone  circuits,  it  will  be  seen 
that  circuits  C  and  D  are  not  subject  to  cross  talk  from  circuit  B,  and 
vice  versa;  but  circuits  C  and  D  are  each  transposed  at  the  same 
place,  and  with  respect  to  each  other  are  not  transposed  at  all.  In 
Fig.  213  are  shown  the  conditions  assumed  in  Fig.  212,  with  the  tele- 
phone transpositions  corrected  so  as  to  eliminate  both  the  cross  talk 


344  TOLL  TELEPHONE  PRACTICE 

between  the  telephone  circuits  and  the  disturbing  induction  from  the 
power  circuit. 

The  transposition  of  telephone  lines  for  the  elimination  of  mutual 
disturbances,  as  well  as  the  prevention  of  disturbances  from  power 
circuits,  was  considered  from  both  theoretical  and  practical  stand- 
points by  Mr.  F.  F.  Fowle  in  a  paper  read  before  the  Association  of 
Railway  Telegraph  Superintendents  in  May,  1903;  and  again  before 


X 


FIG.  213.  —  Example  of  Correct  System  of  Transposition,  Correcting  the  Faults 

Shown  in  Fig.  212. 

the  American  Institute  of  Electrical  Engineers  in  October,  1904. 
These  papers  have  been  drawn  upon  freely  in  the  following  discussion 
of  the  general  problem. 

In  the  transposition  of  telephone  lines  it  is  very  essential  to  adopt 
a  certain  standard  length  of  section  within  which  all  the  wires  shall 
be  transposed,  and  the  mutual  disturbances  eliminated.  The  general 
"procedure  is  a  consecutive  application  of  the  standard  section,  com- 
mencing at  either  end  of  the  line;  this  will  continue  until  some  inter- 
mediate junction  point  or  the  opposite  terminus  is  reached.  The 
line  length  is  seldom  an  exact  multiple  of  the  section  length;  if  the 
remainder  is  less  than  half  a  section,  it  is  added  to  the  preceding 
section,  or  if  greater  than  a  half-section,  it  is  made  a  complete  section 
by  itself.  In  either  case  the  standard  section  is  extended  or  shortened 
to  suit  the  requirements. 

The  treatment  of  induction  between  telephone  circuits  has  been 
by  empirical  rule  rather  than  theory.  It  has  been  determined  by 
experiment,  with  transmitters  and  receivers  of  a  given  power,  how 


CROSS  TALK  AND   INDUCTIVE  DISTURBANCES 


345 


frequently  two  adjacent  circuits  should  be  transposed  in  order  to 
eliminate  cross  talk.  In  two-mile  sections  transposed  at  the  center, 
it  will  be  found  that  the  cross  talk  is  distinguishable  with  transmission 
sufficiently  powerful  for  icoo-mile  service.  However,  one-half  or 
one-quarter  mile  sections  transposed  at  the  center  are  satisfactory, 
where  the  minimum  transposition  spacing  is  one-quarter  mile.  The 
existence  of  cable  at  each  end  of  the  line,  to  any  considerable  length, 
will  reduce  cross  talk,  which  can  be  accounted  for  by  the  fact  that 
the  attenuation  in  the  cable  diminishes  the  strength  of  the,  cross  talk 
currents  which  come  from  the  distant  open-wire  line. 

The  first  step  in  developing  a  standard  section  is  that  of  devising 
different  types  of  transposed  circuits.  The  manner  in  which  this  is 
readily  accomplished  is  shown  in  Fig.  214.  It  will  be  observed  from 


SABACABAD.      A        B        A        C        A        B         u       E 


FIG.  214.  —  Derivations  of  Standard  Transposition  Types. 


the  figure  that  the  exposure  of  circuit  i  to  circuit  2  is  one-quarter ;  of 
i  to  3,  one-quarter;  and  that  of  2  to  3,  one-half.  The  increased  ex- 
posure of  circuit  2  to  circuit  3  is  due  to  the  fact  that  two  transpositions 
on  circuit  2  are  identical  in  location  with  the  end  transpositions  on 
circuit  3;  therefore,  these  transpositions  have  no  beneficial  effect  as 
regards  the  inductive  action  between  the  circuits.  It  will  be  further 


346 


TOLL  TELEPHONE  PRACTICE 


observed  that  the  exposure  of  circuits  i  to  5,  2  to  6  and  3  to  7  is 
one-eighth;  while  that  of  2  to  8  and  2  to  9  is  one-sixteenth,  etc.  A 
complete  list  of  the  exposures  is  given  in  terms  of  the  length  of  a 
transposition  section  in  Table  14. 

TABLE  14 

CROSS-TALK  EXPOSURES  IN  TERMS  OF  STANDARD  TRANSPOSITION 

SECTIONS ' 


To 

i 

2 

3 

4 

5 

6 

7 

8 

9 

10 

ii 

12 

13 

14 

2 

V4 

3 

V4 

V2 

4 

Vs 

Ys 

Vs 

5 

% 

Vs 

Vs 

V2 

6 

Vs 

Vs 

Vs 

% 

V4 

7 

% 

Vs 

Vs 

V4 

V4 

V4 

8 

He 

Vie 

Vie 

Vie 

Vie 

Vie 

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9 

He 

Vie 

Vie 

He 

Vie 

He 

He 

V2 

10 

Vie 

Vie 

Vie 

Me 

Vie 

He 

Vie 

V4 

V4 

ii 

Vie 

Vie 

Vie 

Vie 

He 

He 

Vie 

V4 

V* 

V2 

12 

Vie 

Vie 

Vie 

Vie 

He 

He 

He 

Vs 

Vs 

Vs 

Vs 

13 

Vl6 

Vl6 

Vl6 

Vie 

He 

He 

Vie 

Vs 

Vs 

Vs 

Vs 

V2 

14 

Vie 

Vie 

Vie 

Vie 

He 

He 

Vie 

Vs 

Vs 

Vs 

Vs 

V4 

V* 

IS 

Vl6 

Vie 

Vie 

He 

Vie 

Vie 

Vie 

Vs 

Vs 

Vs 

Vs 

V4 

V* 

V2 

The  derivation  of  the  types  is  quite  simple  and  is  shown  at  the 
right  in  Fig.  214.  The  first  three  of  these  are  necessarily  obvious. 
The  fourth,  as  indicated,  is  obtained  by  doubling  the  number  of  trans- 
positions in  the  second;  the  fifth  by  superimposing  the  first  on  the 
fourth;  and  the  sixth  by  superimposing  the  second  on  the  fourth. 
The  absolute  length  of  exposure  depends  entirely  upon  the  selection 
of  the  length  of  the  section.  Having  given  the  maximum  permissible 
exposure,  the  length  of  section  depends  upon  the  number  of  trans- 
position types  required  to  take  care  of  the  ultimate  number  of  circuits 
on  the  pole  line.  For  convenience  the  exposure  should  be  an  integral 
multiple  of  the  span  length.  A  satisfactory  standard  of  exposure 
between  two  adjacent  horizontal  circuits  on  a  ten-pin  cross-arm  is  one- 
quarter  mile  between  transpositions.  If  two  such  adjacent  circuits 
are  transposed,  with  respect  to  each  other,  one-quarter  mile  from  one 
of  the  terminals  and  then  at  each  consecutive  half-mile  to  the  distant 
terminal,  it  will  be  found  that  with  the  standard  of  transmission  now 
in  general  use,  the  cross  talk  will  be  entirely  negligible  under  normal 
conditions.  An  eight-mile  section  has  been  extensively  used,  but  is 
rather  long;  a  length  of  four  miles  is  much  more  convenient.  In  case 


CROSS  TALK  AND   INDUCTIVE  DISTURBANCES 


347 


there  are  only  a  few  circuits  a  two -mile  section  may  be  used;  a  case 
of  this  kind  would  be  a  ten-wire  line  on  a  single  cross-arm,  as  shown 
in  Fig.  215.  In  the  application  of  a  standard  section  to  any  line,  it 
is  well  to  remember  the  general  rule,  by  reason  of  which  any  discontin- 
uity in  the  line  is  made  the  junction  of  two  contiguous  sections.  A  dis- 
continuity is  established  whenever  new  or  branch  lines  are  joined  to 


2  3 

Q       Q       9  Q 


Q Q 


•2MIUES- 


FIG.  215.  —  Transposition  Scheme  for  a  Ten-wire  Line. 

the  main  line,  or  when  a  number  of  the  main  line  circuits  leave  the 
main  route.  The  same  condition  of  discontinuity  arises  when  all  or 
any  of  the  circuits  enter  an  intermediate  or  terminal  office. 

Transposition  poles  are  generally  placed  at  one-quarter  mile  inter- 
vals, or  every  ten  spans.  The  standard  span  is  130  feet  and  the  trans- 
position poles  are  consequently  1300  feet  apart.  The  general  system 
which  has  been  adopted  and  used  by  the  American  Telephone  and 
Telegraph  Company  is  shown  in  Figs.  216  and  217.  The  system 
indicated  in  Fig.  216  is  arranged  for  two  cross-arms,  each  of  which 
carries  six  wires  or  three  circuits.  Fig.  217  shows  four  cross-arms, 
each  of  which  is  equipped  with  five  circuits.  In  order  that  proper 
construction  records  may  be  maintained,  each  pin  is  numbered.  The 
method  of  numbering  the  wires  on  a  ten-pin  arm  is  shown  in  Fig.  217; 
for  an  eight-pin  arm  the  wires  5  and  6  are  omitted  and  the  remaining 
wires  are  numbered  i  to  10  on  the  upper  and  n  to  20  on  the  lower 
cross-arm.  The  numbering  of  the  wires  on  a  six-pin  arm  is  shown  in 
Fig.  216,  which  follows  the  basis  of  a  ten-pin  arm.  On  four-pin  arms 
the  wires  next  to  the  pole  and  the  two  outside  wires  on  each  arm  are 
omitted,  the  numbering  being  otherwise  the  same.  The  system  of 
numbering  for  four  cross-arms  is  shown  in  Fig.  217. 

Figs,  216  and  217  each  show  one  complete  standard  section  which 


348 


TOLL  TELEPHONE  PRACTICE 


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TOLL  TELEPHONE  PRACTICE 


contains  thirty- two  transposition  poles,  separated  by  equal  distances 
of  1300  feet  or  one-quarter  of  a  mile.  Transposition  sections  may 
be  standard  or  special.  A  standard  section  is  41,600  feet  long;  but 
a  special  section  may  be  anywhere  from  21,000  to  62,000  feet  long,  in 
which  the  transposition  poles  will  be  spaced  at  intervals  of  one  thirty- 
second  of  the  length  of  the  section. 

Transposition  poles  are  usually  located  when  the  line  is  measured 
and  the  poles  are  stenciled,  proceeding  continuously  from  one  end  of 
the  line  to  the  other.  The  end  section  at  a  junction,  intermediate 
office,  or  terminal  is  treated  as  before  described.  The  pole  lettering 
follows  Figs.  216  and  217. 

On  all  standard  sections,  as  will  be  observed  from  Figs.  216  and 
217,  the  distance  from  the  first  open- wire  fixture  to  the  first  A  pole  is 


FIG.  218.  —  A-B-C  Transposition  System. 

1300  feet;  that  to  the  first  B  pole  2600  feet;  to  the  first  C  pole,  5200 
feet;  to  the  first  D  pole,  10,400  feet;  to  the  first  E  pole,  20,800  feet; 
and  to  the  first  S  pole,  or  the  end  of  the  section,  41,600  feet.  Count- 
ing from  the  first  A  pole,  every  alternate  transposition  pole  is  an  A 
pole.  Counting  from  the  first  B  pole,  every  fourth  transposition 
pole  is  a  B  pole.  Counting  from  the  first  C  pole,  every  eighth  trans- 
position pole  is  a  C  pole.  Counting  from  the  first  D  pole,  every 
sixteenth  transposition  pole  is  a  D  pole.  Counting  from  the  first  E 
pole,  every  thirty-second  transposition  pole  is  an  E  pole.  Counting 
from  the  first  open-  wire  fixture,  every  thirty-second  transposition  pole 
pole. 


s  an 


The  system  just  described  is  generally  known  as  the  "  Standard 


CROSS  TALK  AND  INDUCTIVE  DISTURBANCES  351 

System  of  Transposition."  There  is,  however,  another  method  of 
transposing  which  is  known  as  the  A-B-C  system,  illustrated  in 
Fig.  218.  This  system  was  used  on  the  original  New  York-Chicago 
line,  built  in  1893.  In  the  A-B-C  system  the  transposition  poles 
are  likewise  placed  130x5  feet  apart,  but  there  is  no  definite  section 
in  which  the  mutual  disturbances  are  balanced  and  eliminated,  as  in 
the  standard  system.  The  pole  lettering  is  different  and  the  letters 
represent  different  types  of  transposition  poles.  All  the  odd-num- 
bered cross-arms  are  transposed  in  a  manner  similar  to  the'top  cross- 
arm  and  the  even-numbered  arms  like  the  second  cross-arm. 

The  methods  of  making  transpositions  are  quite  numerous.  Fig. 
219  shows  the  standard  method  when  it  is  possible  to  pull  up  sufficient 
slack  at  the  transposition  pole.  For  this  purpose,  six  feet  of  slack 
should  be  taken  up  by  means  of  the  blocks  and  come-alongs  shown 
at  M  in  Fig.  219;  this  should  then  be  cut  so  as  to  leave  ends  projecting 
20  inches  beyond  the  cross-arm,  on  the  pole  side  of  the  arm.  The 
next  step  is  to  slip  on  the  half-sleeves  C  and  D  and  dead-end  the  wires 
X  and  Z,  leaving  loose  ends  projecting  for  the  sleeves  G  and  H.  The 
half -sleeves  E  and  F  should  then  be  slipped  on  the  opposite  ends  and 
wires  dead-ended,  as  shown.  The  next  and  last  step  is  to  put  on  the 
half -sleeves  G  and  H,  when  the  transposition  is  completed.  When 
pole  wires  are  being  transposed,  the  cross  connections  should  be 
brought  back  around  the  insulator  as  shown  at  0  in  Fig.  219;  if  both 
wires  are  on  the  same  side  of  the  pole,  the  connections  should  be 
arranged  as  at  N.  In  making  these  transpositions,  it  should  be 
remembered  that  the  transposition  insulator  shown  in  Fig.  178,  and 
the  transposition  pin  shown  in  Fig.  149,  must  be  used. 

When  slack  is  not  available,  the  standard  transposition  should  be 
made  as  indicated  in  Fig.  220.  Here  the  line  wires  should  be  cut  on 
the  pole  side  of  the  cross-arm,  20  inches  from  the  pin.  The  half- 
sleeves  C  and  D  should  then  be  slipped  over  the  line  wires  and  the 
circuit  dead-ended,  while  the  ends  of  the  wire  are  allowed  to  project 
for  the  sleeves  G  and  H.  Six  feet  of  slack  wire  is  next  cut  into  the 
line  on  the  pole  side  of  the  circuit  by  means  of  the  sleeves  A  and  B. 
The  half-sleeves  E  and  F  are  slipped  over  the  slack  ends  and  then  the 
circuit  is  pulled  up  and  dead-ended,  as  shown  in  the  figure.  The 
half-sleeves  G  and  H  are  used  to  make  the  cross  connections  and  the 
transposition  is  finally  completed.  If  the  transposition  is  made  on 
pole  wires,  the  connections  should  be  brought  back  around  the  insu- 


352 


TOLL  TELEPHONE  PRACTICE 


REGULAR 
TRANSPOSITION 


FIG.  219.  —  Method  of  Cutting  in  Transpositions  With  Slack. 


CROSS  TALK  AND   INDUCTIVE   DISTURBANCES 


353 


lator  as  shown  at  0.     The  cross  connections  at  a  transposition  afford 
a  very  convenient  place  to  insert  test  connectors,  so  that  the  line  can 

A 


FIG.  220.  —  Standard  Method  of  Cutting  in  Transpositions. 


FIG.  221.  —  Method  of  Installing  Test  Connectors. 

be  opened  for  testing  purposes  without  cutting  the  wires.  One  of 
these  connectors  of  the  Cook  type  is  shown  in  Fig.  221.  They 
are  sometimes  installed  as  a  substitute  for  a  lineman's  test  station, 
or  at  points  where  testing  is  occasionally  required.  Transpositions 


354  TOLL  TELEPHONE  PRACTICE 

sometimes  introduce  cases  of  trouble  caused  by  crosses  between  the 
connections.  In  order  to  minimize  this,  the  wires  W  and  Z  should  be 
dead-ended  in  the  top  grooves  of  the  insulators  and  leads  X  and  F 
in  the  bottom  grooves,  as  shown  in  Figs.  219  and  221. 

In  cutting  in  transpositions,  the  half -sleeves  should  be  given  one 
and  one-half  twists  and  the  whole-sleeves  three  twists ;  and  in  twisting 
the  sleeves  at  a  dead-end,  the  stationary  connector  should  always  be 
held  at  the  insulator  end  of  the  sleeve,  so  as  to  throw  the  twist  out 
into  the  span,  while  for  the  sleeves  G  and  H,  the  stationary  connector 
should  be  placed  at  the  line-wire  end  of  the  sleeve. 

Ordinarily  a  pole  line  must  be  fully  transposed  before  it  is  placed 
in  service.  Sometimes,  however,  transpositions  are  cut  in  afterwards, 
especially  in  connection  with  the  installation  of  phantom  circuits. 
This  always  interferes  with  the  service  slightly,  being  most  serious  in 
the  case  of  morse  leases.  Another  feature,  also,  is  worth  mentioning, 
in  connection  with  the  numbering  of  line  wires  at  the  test  panels. 
The  insertion  of  a  single  transposition,  as  shown  at  E  in  Fig.  222, 
reverses  the  pair.  Confusion  is  likely  to  exist  while  the  work  is  under 


i'e 


?•  2.        I  I        2.  Z.       I  T 

FIG.  222.  —  Reversal  of  Line  Wires  Caused  by  Cutting  in  a  New  Transposition. 

way,  but  the  numbering  system  is  readily  corrected  when  the  work  is 
completed  by  making  the  necessary  reversals  at  the  main  frames. 

Another  form  of  transposition  now  used  very  widely  is  known, 
because  of  its  construction,  as  the  single-pin  transposition.  This  type 
is  shown  in  Fig.  223,  where  A,  B  and  C  represent  the  cross-arms  on 
consecutive  poles.  Cross-arms  A  and  C  are  each  equipped  with 
standard  insulators  in  the  usual  way,  while  cross-arm  B  has  one  trans- 
position insulator  per  circuit.  The  circuit  is  transposed  by  stringing 
wire  number  i  from  pin  G  on  cross-arm  A  to  the  lower  groove  in  the 
transposition  insulator,  and  then  to  pin  E  on  cross-arm  C.  Wire 
number  2  of  the  circuit  is  carried  from  pin  F  on  cross-arm  A  to  the 
upper  groove  of  the  transposition  insulator  and  then  to  pin  D  on  cross- 
arm  C.  This  rotates  the  circuit  through  180  degrees,  or  reverses  the 
relative  position  of  the  two  line  wires.  Fig.  224  indicates  how  this 


CROSS  TALK  AND   INDUCTIVE  DISTURBANCES 


355 


transposition  is  cut  in;  slack  is  needed  in  only  one  wire,  instead  of 
both. 

The  relative  merits  of  this  type  of  transposition,  as  stated  by  Mr. 
Fowle  in  his  papers  previously  referred  to,  are  as  follows:  "It  has 


FIG.  223.  —  Single-pin  Transpositions. 

the  comparative  advantages  of  less  first  cost  and  simpler  construction. 
It  can  be  cut  in  at  any  time,  cut  out,  or  moved  several  poles  at  less 
cost  and  with  much  less  work  than  yi  the  case  of  a  square  transposition. 
If  transpositions  occur  frequently,  every  one-half  or  one-quarter  mile, 


FIG.  224.  —  Method  of  Cutting  in  Single-pin  Transposition. 

the  line  capacity  is  increased  a  few  per  cent  and  the  line  inductance 
diminished,  with  a  consequent  slight  increase  in  attenuation.  The 
square  transposition  has  the  advantage  of  concentrating  the  entire 
transposition  within  a  very  short  length  and  of  not  altering  the  plane 
or  the  separation  of  the  wires.  While  the  single-pin  transposition 


356  TOLL  TELEPHONE  PRACTICE 

changes  the  plane  of  the  circuit,  the  wire  separation  is  greatly  reduced, 
and  this  is  an  advantage.  Since  it  requires  two  spans  in  which  to 
make  this  transposition,  it  is  possible  to  transpose  only  at  every  other 
pole,  as  a  maximum,  in  case  of  excessive  induction,  against  every  pole 
for  the  square  transposition." 

The  practical  application  of  transpositions  has  been  considered, 
thus  far,  only  with  reference  to  cross  talk  between  physical  metallic 
circuits.  The  rapid  development  of  phantom  circuits  during  the  past 
few  years  has  added  a  new  and  somewhat  complicated  element  to  the 
general  problem.  Phantom  circuits,  if  not  transposed,  will  cross  talk 
in  the  same  manner  as  physical  circuits.  This  can  be  prevented,  as 
before,  by  a  suitable  system  of  transpositions  of  the  physical  circuits 
composing  the  phantoms. 

There  are  three  possible  types  of  phantom  circuit  transpositions. 
In  the  first,  shown  in  Fig.  225,  the  phantom  circuit  is  transposed,  and 


FIG.  225.  —  First  Type  of  Phantom  Transpositions. 

the  two  physical  circuits,  while  not  transposed  with  respect  to  each 
other,  are  transposed  with  respect  to  all  other  parallel  circuits.  The 
second  method,  indicated  in  Fig.  226,  causes  transpositions  of  the 
phantom  and  one  of  the  physical  circuits;  and  now  the  two  physical 
circuits  are  transposed  with  respect  to  each  other.  In  this  type,  also, 

4 -.          > 1 

x^ 

, /  XN 3 

2 /      V_ 4 

FIG.  226.  —  Second  Type  of  Phantom  Transpositions. 

one  of  the  physical  circuits  is  transposed  with  respect  to  all  other 
parallel  circuits,  whereas  the  other  is  not.  In  the  last  or  third  type, 
shown  in  Fig.  227,  the  phantom  circuit  is  transposed  but  neither  one 
of  the  physical  circuits  is  transposed  with  respect  to  any  parallel  cir- 
cuits, although  they  are  transposed  with  respect  to  each  other.  In 


CROSS  TALK  AND  INDUCTIVE  DISTURBANCES 


357 


case  the  regular  transposition  sections  are  not  too  long,  the  phantom 
transpositions  may  be  located  at  the  poles  forming  the  junctions 
between  sections,  where  they  will  have  no  effect  on  the  regular  sec- 
tional system.  If  placed  within  a  section,  however,  they  will  upset 
the  exposures  shown  in  Fig.  213.  If  many  phantom  circuits  are 
employed,  it  is  best  to  lay  out  a  section  with  only  the  phantom  trans- 


FIG.  227.  —  Third  Type  of  Phantom  Transpositions. 

positions  and  then  superimpose  the  additional  transpositions  required 
to  eliminate  cross  talk  between  the  physical  circuits.  In  general,  it 
will  be  necessary  to  change  the  previous  systems  somewhat,  cutting 
out  some  of  the  transpositions  and  cutting  in  others.  It  is  general 
practice  to  compose  the  phantom  circuits  of  pairs  1-2  and  3-4,  7-8 
and  9-10,  and  corresponding  pairs  on  the  lower  cross-arms.  The 
arrangement  of  the  A-B-C  system,  in  this  manner,  is  shown  in  Fig.  228. 


FIG.  228.  —  Phantom  Transposition  Applied  to  the  A-B-C  System. 

Fig.  229  shows  a  forty- wire  line  transposed  according  to  the  standard 
system  and  arranged  for  eight  phantom  circuits. 

In  the  transposition  layouts  shown  in  Figs.  228  and  229,  each  of 
the  three  types  of  phantom  transpositions  shown  in  Figs.  225,  226 
and  227  is  used.  This  makes  the  work  of  installation  somewhat 


358 


TOLL  TELEPHONE  PRACTICE 

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CROSS  TALK  AND   INDUCTIVE  DISTURBANCES 


359 


FIG.  230.  —  Construction  of  Phantom  Transposition;  First  Type,  Standard  Method. 


FIG.  231.  —  Method  of  Cutting  Standard  Transpositions  to  Change  to  the  First  Type  of 

Phantom  Transposition. 


36° 


TOLL  TELEPHONE  PRACTICE 


complicated,  and  it  should  be  executed  with  great  care  to  avoid  con- 
fusion and  mistakes.  The  following  description  outlines  the  practice 
of  the  American  Telephone  and  Telegraph  Company. 


Q 


n 


FIG.  232.  —  Cleat  Wiring  in  First  Type  of  Phantom  Transposition. 

When  both  physical  circuits  are  already  transposed  by  the  double- 
pin  method,  the  phantom  transposition  should  be  made  as  shown  in 
Fig.  230.  The  best  way  to  make  the  change  from  the  regular  to  the 


FIG.  233.  —  End  View  of  Cleat  Wiring. 

phantom  transposition,  is  to  cut  the  wires  of  the  old  transpositions 
at  L,  M,  N  and  0  as  shown  in  Fig.  231.  The  sleeves  near  M  and  0 
should  then  be  cut  off.  The  four  connections  are  then  carefully 


CROSS  TALK  AND   INDUCTIVE  DISTURBANCES 


361 


twisted  over  and  connected,  by  means  of  two  half-sleeves,  between 
the  middle  wires  as  shown  in  Fig.  230.  The  two  outer  wires  are  trans- 
posed by  means  of  two  pieces  of  insulated  wire  about  five  feet  long, 
which  are  wired  in  cross-arm  cleats  attached  to  the  under  side  of  the 
cross-arm.  These  cleats  should  be  fastened  just  inside  of  the  two 
outer  pin-holes,  as  shown  in  Fig.  232.  The  insulated  wire  should  be 
run  in  the  outside  holes  of  the  cleats,  and  should  be  soldered  to  the 


FIG.  234.  —  Construction  of  Phantom  Transposition;   First  Type,  Single-pin  Method. 

line  wires  between  the  insulators  and  the  half-sleeves.  The  insulated 
wires  should  cross  each  other  under  the  pin  farthest  from  the  pole, 
as  illustrated  in  Fig.  233. 

In  case  the  two  physical  circuits  are  already  transposed  by  the 
single-pin  method,  the  phantom  transposition  should  be  made  as  indi- 
cated in  Fig.  234.  Here  the  middle  wires  are  cut  at  A,  B,  C  and  D, 
about  12  inches  from  the  insulators.  Two  pieces  of  line  wire  about 
four  feet  long  are  then  cut  into  the  two  middle  wires,  by  means  of 
the  whole  sleeves  E,  F,  G  and  H,  and  a  standard  single -pin  trans- 
position made.  The  two  outer  wires  are  then  transposed  as  before, 
by  means  of  insulated  wire  in  cleats. 

When  the  two  physical  circuits  are  not  already  transposed,  the 
phantom  transposition  is  made  as  outlined  in  Fig.  235.  In  this  case, 
the  middle  wires  are  transposed  according  to  the  single-pin  method. 
One  of  these  wires  is  cut  at  D,  20  inches  from  the  insulator  and  the 
other  at  C,  12  inches  from  the  insulator.  Into  the  latter  is  spliced 
30  inches  of  line  wire  by  means  of  the  whole  sleeve  H,  and  the  free 


362 


TOLL  TELEPHONE  PRACTICE 


ends  of  the  wires  are  then  connected  by  means  of  the  sleeves  G  and  J. 
The  outer  wires  are  cut  at  A  and  B  about  12  inches  from  the  insulators, 
and  30  inches  of  slack  is  spliced  into  two  of  the  ends  by  means  of  the 
sleeves  E  and  F.  The  four  free  ends  are  then  dead-ended  by  means 


FIG.  235.  —  Construction  of  Phantom  Transposition;  First  Type,  Where  no  Previous 

Transposition  Existed. 

of  half-sleeves  in  the  standard  manner  and  the  transposition  is  com- 
pleted with  rubber-covered  wire  and  cross-arm  cleats,  as  previously 
described. 

In  the  second  type  of  phantom  transposition,  only  one  of  the  physical 
circuits  is  transposed.  The  wires  of  the  circuit'which  is  not  transposed 
are  dead-ended  on  the  bottom  grooves  of  the  insulators  and  those  of 
the  other  circuit  on  the  upper  grooves,  as  illustrated  in  Fig.  236. 
The  alternate  wires  on  opposite  sides  of  the  cross-arm  should  be  cut 
20  inches  from  the  insulators,  as  indicated  in  the  figure,  and  about 
seven  feet  of  slack  cut  into  two  of  the  short  ends  by  means  of  sleeves 
A  and  Z>,  and  about  six  feet  in  the  remaining  two  with  the  sleeves 
B  and  C.  Before  the  wires  are  dead-ended,  the  half-sleeves  E,  F,  H 
and  /  should  be  slipped  over  proper  ends.  Then  the  slack  end  of 
wire  A  should  be  bent  around  the  groove  of  the  insulator  and  made 
fast  in  the  half-sleeve  E,  about  ten  inches  from  the  insulator.  The 
end  from  D  is  attached  to  the  sleeve  F  in  a  like  manner,  while  the 
end  from  C  is  carried  around  the  insulator  and  connected  to  the  end 
from  B  by  means  of  the  half-sleeve  G.  In  order  that  the  connection 
from  I  to  H  shall  not  foul  with  the  other  wires  of  the  transposition, 


CROSS  TALK  AND   INDUCTIVE   DISTURBANCES 


363 


a  bracket  equipped  with  a  standard  insulator  is  attached  to  the  same 
side  of  the  cross-arm  as  the  sleeve  C,  between  the  middle  pins.  This 
bracket  should  be  so  located  that  the  groove  of  the  insulator  is  at 
least  three  inches  above  the  adjacent  wires.  A  six-foot  length  of  wire 
is  then  attached  to  the  outside  line  by  means  of  the  half -sleeve  /; 


FIG.  236.  —  Construction  of  Phantom  Transposition;  Second  Type. 

this  wire  is  next  carried  around  the  groove  of  the  transposition  insu- 
lator and  thence  to  the  bracket  insulator,  about  which  it  is  given  one 
turn,  when  it  is  drawn  up  as  tightly  as  possible  and  terminated  in  the 
half-sleeve  H. 

In  the  third  type  of  phantom  transposition,  in  which  neither  physical 
circuit  is  transposed,  the  alternate  wires  on  opposite  sides  of  the  cross- 
arm  are  cut  about  20  inches  from  the  insulator  and  seven  feet  of  slack 


TOLL  TELEPHONE  PRACTICE 


is  cut  into  the  short  ends  by  means  of  the  sleeves  A,  B,  C  and  Z),  as 
indicated  in  Fig.  237.  The  half-sleeves  E,  F,  G  and  H  are  then 
slipped  over  the  proper  ends,  before  the  wires  are  dead-ended.  The 
wires  which  constitute  a  continuous  circuit  are  dead-ended  in  similar 
grooves  of  the  insulators.  The  ends  from  sleeves  A  and  D  are  then 


FIG.  237.  —  Construction  of  Phantom  Transposition;  Third  Type. 

bent  back  around  the  insulator  grooves  and  attached  to  the  half- 
sleeves  E  and  F,  respectively,  ten  inches  from  the  insulators.  These 
wires  must  be  drawn  taut  before  the  sleeves  are  twisted.  The 
ends  from  B  and  C  are  then  bent  around  the  insulator  grooves  and 
fastened  to  the  half-sleeves  H  and  G,  respectively. 

The  transposition  methods  employed  in  dealing  with  disturbances 
from  power  circuits  comprise  the  remaining  phase  of  the  subject. 
Mr.  F.  F.  Fowle  in  his  paper  before  the  American  Institute  of  Electrical 


CROSS  TALK  AND   INDUCTIVE  DISTURBANCES 


365 


Engineers,  previously  referred  to,  treated  this  subject  quite  exten- 
sively, and  what  follows  is  largely  abstracted  from  that  source. 

When  telephone  lines  are  paralleled  by  power  lines  the  transposition 
problem  naturally  becomes  more  complicated,  and  the  development 
of  high-tension  transmission  is  increasing  so  rapidly  that  this  branch 
of  the  subject  of  transposition  is  exceedingly  important.  In  this  case 
it  is  necessary  to  recognize  not  only  the  manner  in  which  the  load  is 
distributed  in  the  disturbing  circuits,  producing  abrupt  changes  in  line 
pressure  or  line  current,  but  also  any  changes  in  the  wire  spacing. 
Thus,  if  the  length  L  of  the  circuits  shown  in  Fig.  238  is  not  very  great 
there  will  be  practically  no  mutual  interference.  The  per  cent  of 


A 

B 

POWER  CIRCUIT 

TELEPHONE  CIRCUIT                          / 

/ 
\ 

*—-  l_                                                                    -  > 

FIG.  238.  —  Single  Exposure  of  Telephone  Circuit  to  Power  Circuit. 

pressure  drop  in  the  power  circuit  must  be  so  small  that  the  total 
induced  charges  on  the  portion  AB  are  sensibly  equal  and  opposite 
to  those  on  BC\  likewise,  the  per  cent  of  current  loss  in  the  power 
circuit  must  be  so  small  that  the  induced  E.M.F.  in  the  portion  AB 
is  equal  and  opposite  to  that  in  BC.  However,  if  a  transformer  or  a 
branch  circuit  be  connected  to  the  power  circuit  within  the  portion 
AC,  the  transposition  will  no  longer  neutralize  the  induction.  If  the 
transformer  were  placed  at  B,  the  transposition  would  have  the  least 
effect,  for  the  point  B  on  the  telephone  circuit  is,  as  it  were,  a  neutral 
point.  Should  the  power  circuit  be  a  constant-current  circuit,  any 
arc  lamp  which  is  cut  into  the  line  will  have  the  same  effect  as  regards 
the  efficiency  of  the  transposition.  Any  change  in  the  wire  spacing 
of  the  power  circuit  will  also  modify  the  effect  of  the  transposition. 

Therefore  that  portion  of  the  disturbing  line  within  which  the 
E.M.F.  and  the  current  are  both  constant  as  to  magnitude  and  phase, 
should  be  treated  as  a  unit  section  and  all  the  telephone  circuits  should 
be  transposed  opposite  its  center.  If  the  total  external  exposure  to 
the  power  line  involves  several  consecutive  sections,  the  cross-talk 


366 


TOLL  TELEPHONE  PRACTICE 


transpositions  should  be  placed  opposite  the  junctions  of  the  sections, 
where  the  disturbing  current  and  pressure  change  in  magnitude  or 
phase. 


THREE    PHASE 


POWER  CIRCUIT 


TELEPHONE    LINE 


THREE    PHASE 


POWER  CIRCUIT 


B.KC.  ARE    CROSSTALK    TRANSPOSITIONS 
Xt  Ml  LE,    APART 

FIG.  239.  —  Unbalanced  Exposure  of  Telephone  Line  to  Power  Lines. 


This  may  be  illustrated  by  a  reference  to  Figs.  239  and  240.  These 
show  a  telephone  line  paralleled  by  two  three-phase  circuits.  Fig.  239 
shows  the  transpositions  as  they  were  before  the  power  lines  were 


X 

Y 

THREE    PHASE 

POWER  CIRCUIT 

THREE    PHASE 

POWER  CIRCUIT 

X   TELEPHONE    LINE             ^ 

(            X 

n° 

ALL  TELEPHONE     LINES  ARE    TR/ 

B                        T 
.NSPOSED  AT  T. 

FIG.  240.  —  Method  of  Balancing  the  Exposures  Shown  in  Fig.  239. 

built;  after  these  lines  were  placed  in  service  there  was  considerable 
induction.  The  layout  which  eliminated  the  induction  entirely  is 
shown  in  Fig.  240,  in  which  XY  and  YZ  are  each  treated  as  unit 


CROSS  TALK  AND  INDUCTIVE  DISTURBANCES 


367 


sections  with  a  transposition  T  at  the  center,  where  all  telephone  cir- 
cuits are  transposed.  To  simplify  the  drawing  only  one  telephone 
circuit  is  shown  in  the  figures.  The  cross-talk  transpositions  for  this 
circuit  remain  the  same  in  both  figures,  and  this  is  naturally  true  of 
all  the  others.  A  more  general  case,  depicted  in  Fig.  241,  further 


;          '  i>                          '              ^ 

w  ^ 

* 

2 

1 

£    5         ^ 

)o 

B 

|  V 

I                        E 

if                   > 

C               X 

X                ) 

:           x 

T 

r             T 

T 

r           T 

FIG.  241.  —  General  Type  of  Balanced  Exposure. 

illustrates  the  method  of  selecting  the  proper  sections  and  the  locations 
of  the  transpositions  T  which  eliminate  the  induction  from  the  power 
circuit. 

The  general  scheme  just  outlined  is  exceedingly  efficient,  until 
the  character  of  the  exposure  becomes  very  complicated.  Then  the 
transpositions  may  become  so  frequent  as  to  be  impractical,  or  the 
physical  limitations  may  be  such  as  to  prevent  their  proper  location. 
Thus,  if  the  connected  load  on  the  power  circuit  is  developing  rapidly, 
the  exposures  will  be  changing  frequently,  due  to  new  customers. 
A  remedy  for  this  would  be  twisted  pairs  or  a  cable;  but,  as  previously 
shown,  either  of  these  would  impair  the  transmission.  A  study  of 
the  power  wires  should  be  made  with  a  view  of  ascertaining  whether 
they  are  not  separated,  with  respect  to  one  another,  further  than  is 
necessary  with  the  pressure  employed,  or  whether  the  separations  are 
uniform.  Thus  there  are  cases  in  which  the  reduction  of  the  sepa- 
ration from  several  feet  to  less  than  two  feet  has  so  reduced  the  field 
of  the  power  circuit  as  to  allow  the  cross-talk  transpositions  to  prac- 
tically eliminate  the  induction. 

Where   telephone   lines  have  paralleled   transmission   lines   along 


368 


TOLL  TELEPHONE  PRACTICE 


highways,  separated  by  15  or  20  feet,  or  the  width  of  the  highway, 
the  following  practice  has  been  employed;  all  the  telephone  circuits 
are  transposed  at  every  tenth  pole,  midway  between  the  regular 
transpositions,  thus  having  no  effect  upon  the  cross- talk  exposures. 
This  method  is  of  course  a  makeshift,  but  is  sometimes  the  only 
alternative  when  the  exposure  between  the  lines  varies  considerably, 
on  account  of  the  character  of  the  right  of  way. 

Frequently  high-tension  systems  are  transposed  for  their  own  bene- 
fit. When  telephone  circuits  are  run  on  such  pole  lines,  the  trans- 
positions in  the  power  circuits  may  sometimes  be  used  to  reduce  the 
induction;  but  in  general  it  is  best,  regardless  of  the  location  of  the 
telephone  circuits,  to  treat  such  transpositions  as  neutral  points  or 
junctions  of  contiguous  sections.  In  general,  the  induction  from  a 
three-phase  line  is  slightly  greater  than  from  a  single-phase  line  having 
the  same  wire  spacing  and  current  per  wire,  and  a  pressure  equal  to 
the  delta  pressure. 

A  three- wire,  three-phase  line  will  have  two  transpositions  within 
a  section  as  shown  in  Fig.  242,  in  which  two  complete  sections  are 


\ 

/                 N 

( 

V           Y 

) 

/ 

V 

K          K 

„„            I                  

i 

<—  tu-J 

—  s1  

FIG.  242.  —  Transposition  of  Three-wire  Three-phase  Line. 

shown.  It  seems  to  be  fairly  general  practice  to  transpose  high- 
pressure  systems,  but  the  length  of  the  sections  is  usually  several 
miles.  On  this  account,  it  is  difficult  to  make  use  of  the  power-line 
transpositions  in  transposing  the  telephone  line,  and  hence  it  is  usually 
necessary  to  treat  them  as  the  junction  point  between  adjacent  sec- 
"  tions.  On  account  of  the  very  low  frequency  and  the  high  ratio  of 
pressure  to  current  customary  in  high-tension  practice,  there  is  usually 
little  inductive  interference  if  the  power  circuit  is  separated  from  the 
telephone  line  by  the  width  of  the  road  or  highway,  or  say  30  or  40 
feet,  because  the  regular  cross-talk  transpositions  are  sufficient  for  all 
practical  purposes.  Fig.  242  illustrates  the  method  of  transposing 
any  circuit  containing  three  wires,  which  may  be  considered  as  part 
of  a  distribution  line  on  the  Edison  three- wire  system,  or  a  three-phase 


CROSS  TALK  AND  INDUCTIVE  DISTURBANCES 


369 


transmission  line,  or  a  three-wire  two-phase  line.  If  the  three  wires 
are  spaced  equilaterally,  each  transposition  amounts  to  a  revolution 
of  the  line  through  120  degrees.  Thus  the  telephone  line  is  exposed 
to  three  consecutive  sections  of  the  three-wire  line  in  such  a  manner 
that  the  total  induced  electromotive  force  neutralizes  itself. 

In  general,  the  transposition  of  a  circuit  having  n  wires  will  require 
n  —  i  transpositions,  the  distance  from  one  end  of  the  section  of  ex- 
posure to  the  first  transposition  being  -th  of  the  total  length  of  the 

n 

section;  successive  transpositions  will  occur  at  regular  intervals  of  -th 

n 

of  the  section. 


CHAPTER  XX 
METHODS  OF  TESTING 

CHAPTER  XI  describes  the  equipment  commonly  required  by  a 
toll  wire  chief  to  make  the  line  tests  necessary  in  determining  the 
nature  and  location  of  the  various  sorts  of  trouble  ordinarily  met  in 
everyday  toll  service,  and  the  present  chapter  deals  with  the  use  of 
this  equipment.  The  proper  testing  instruments  and  apparatus  are 
readily  procured,  but  their  proper  use  requires  both  some  theoretical 
knowledge  and  considerable  experience  in  manipulation.  In  addition 
to  this,  an  understanding  of  elementary  algebra  is  often  of  consider- 
able value.  This  is  required  in  the  derivation  of  formulae,  only,  and 
is  not  absolutely  essential;  for  the  use  of  formulae,  when  once  derived, 
requires  only  plain  arithmetic. 

Similar  to  many  other  branches  of  telephony,  the  greater  part  of 
the  knowledge  of  testing  is  acquired  by  actual  experience.  It  is  often 
a  comparatively  simple  matter  to  determine  theoretically  just  how  a 
certain  test  should  be  made,  but  it  usually  requires  some  time  and 
patience  to  become  proficient  in  securing  reliable  and  accurate  results. 
Frequent  repetition,  however,  soon  overcomes  this  deficiency  and 
makes  one  so  familiar  with  the  various  procedures  that  they  become 
almost  second  nature.  Then  again,  one  man  finds  some  given  method 
of  testing  extremely  easy  and  efficient,  whereas  the  next  man  experi- 
ences great  difficulty  in  pursuing  that  method,  but  obtains  results 
that  are  just  as  accurate  by  an  entirely  different  procedure.  There 
are  frequently  several  methods  of  testing  for  a  certain  case  of  trouble 
that  are  available  to  a  resourceful  wire  chief,  the  result  from  any  of 
which  will  lead  to  an  accurate  conclusion,  but  there  is  seldom,  if  ever, 
more  than  one  "  best  way."  However,  it  may  be  well  to  add  that  after 
making  the  test  with  the  best  method,  it  is  often  advisable  to  check 
results  by  another;  and  a  careful  tester  will  always  follow  this  plan. 
Very  often  this  "  best  method  "  requires  testing  equipment  that  is 
not  commonly  found  at  small  toll  stations;  then  a  less  accurate  sub- 
stitute must  be  employed,  unless  some  office  not  too  far  away  is  fully 

370 


METHODS   OF  TESTING 


371 


equipped.  The  prime  requisite  of  a  good  tester  is  a  thorough  under- 
standing of  the  theory  and  applications  of  the  instruments  used,  for 
in  this,  as  in  all  other  work,  a  substantial  knowledge  of  the  tools  with 
which  one  is  working  is  essential  to  the  best  results. 

It  is  fortunate  that  a  very  simple  test  will  often  determine  the  nature 
of  a  case  of  trouble,  for  in  small  toll  stations  the  testing  equipment 
usually  consists  merely  of  a  lineman's  test  set  and  possibly  a  volt- 
meter. This  apparatus  placed  in  the  hands  of  a  man  skilled  in  testing, 
will  give  results  that  could  hardly  be  expected;  and  since  this  apparatus 
has  the  greatest  amount  of  application,  owing  to  the  fact  that  the 
small  toll  stations  greatly  outnumber  the  larger  ones,  it  will  be  dis- 
cussed first. 

The  first  step  in  locating  a  case  of  trouble  is  to  determine  accurately 
its  nature,  and  for  this  reason  it  is  necessary  to  understand  thoroughly 
the  different  classes  of  trouble  to  which  a  telephone  line  is  subject. 
Line  faults  may  be  divided  into  four  general  groups  as  follows: 
grounds,  crosses,  opens  and  foreign  currents.  The  first  of  these  four 
divisions  probably  covers  the  most  troublesome  class  of  faults,  because 
an  unbroken  line  wire  may  have  a  ground  connection  with  or  without 
any  resistance  between  the  wire  and  ground.  If  the  ground  exists 
without  resistance  it  is  termed  a  "  dead  "  ground;  but  if  it  has  an 
appreciable  resistance,  it  is  known  as  a  high-resistance  ground.  These 
two  types  of  grounds  are  more  easily  located  and  rectified,  compara- 
tively speaking,  than  the  swinging  or  intermittent  ground.  The 
difficulty  in  the  latter  case  is  that  the  trouble  can  be  observed  for  very 
short  intervals  only,  since  the  ground  appears  and  disappears  without 
any  apparent  cause,  and  frequently  it  is  not  of  sufficient  duration  to 
allow  the  completion  of  a  satisfactory  test. 

The  second  class  of  trouble,  namely,  crosses,  may  be  of  several 
kinds.  Thus  one  of  the  line  wires  may  be  crossed  with  its  mate,  or 
with  a  wire  of  another  line.  If  the  cross  is  of  the  first  variety  and 
without  resistance,  it  is  known  as  a  "  dead  short  "  or  merely  a  short 
circuit,  whereas  if  it  introduces  resistance,  it  is  known  as  a  high- 
resistance  cross.  As  in  the  case  of  grounds,  there  are  quite  often 
intermittent  crosses. 

In  the  third  group  of  troubles  designated  as  opens,  or  breaks,  a 
great  number  of  external  complications  may  be  encountered,  since  it 
rarely  happens  that  the  two  broken  ends  of  a  wire  hang  clear  of  the 
ground  or  other  wires.  It  is  thus  obvious  that  either  one  of  the  two 


372  TOLL  TELEPHONE  PRACTICE 

classes  of  trouble  previously  enumerated  may  be  again  encountered. 
Then  it  frequently  happens,  also,  that  the  open  is  an  electrical  break 
and  not  a  mechanical  one,  such  as  a  corroded  joint,  which  quite  fre- 
quently results  in  intermittent  trouble  and  is  extremely  annoying. 

In  considering  the  last  group,  or  foreign  current  troubles,  it  should 
be  remembered  that  they  are  sometimes  the  most  formidable  of  all. 
This  trouble  is  brought  about  by  the  existence  of  a  difference  of  poten- 
tial on  the  line  wires,  which  causes  a  flow  of  current  in  the  telephone 
circuit,  usually  of  fluctuating  character.  This  trouble  may  be  brought 
about  by  a  cross,  by  static  discharge,  or  by  electrostatic  or  electro- 
magnetic induction.  The  static  discharges  are  often  met  in  the  north- 
western part  of  the  country,  where  they  are  caused  by  the  chaff  of  the 
wheat  during  the  threshing  season,  and  the  extreme  winds  driving 
the  snow  in  winter. 

In  order  to  present  a  clearer  analysis  of  the  several  classes  of  trouble, 
they  have  been  recapitulated  in  tabular  form  as  follows: 

1.  Grounds. 

(a)  Dead  ground. 

(b)  High-resistance  ground  or  leak. 

(c)  Swinging  or  intermittent  ground. 

2.  Crosses. 

(a)  Short  circuit. 

(b)  High-resistance  cross. 

(c)  Intermittent  cross. 

3.  Opens  or  breaks. 

(a)  Broken  ends  insulated. 

(b)  Broken  ends  grounded. 

(c)  Broken  ends  crossed  with  other  wires. 

(d)  Intermittent  opens. 

4.  Foreign  currents. 

(a)  Crosses. 

(b)  Static. 

(c)  Electrostatic  induction. 

(d)  Electromagnetic  induction. 

The  wire  chief,  upon  receiving  a  report  that  a  line  is  in  trouble, 
should  first  convince  himself  that  the  trouble  actually  exists  on  the 
line;  for  it  often  occurs  that  a  line  is  reported  in  trouble  when  the  fault 


METHODS  OF  TESTING 


373 


really  exists  in  a  cord  or  some  other  part  of  the  switchboard  equipment. 
When  he  has  assured  himself  that  the  trouble  actually  exists,  his  »ext 
step  is  to  determine  whether  the  trouble  is  inside  or  outside,  i.e.,  in 
the  part  of  the  line  from  the  arresters  to  the  switchboard,  or  on  the 
outside  line.  In  case  the  trouble  is  outside,  the  office  end  of  the  circuit 
should  be  disconnected;  then,  by  means  of  the  magneto  test  set,  the 
tester  can  determine  whether  either  side  of  the  line  is  grounded.  This 


FIG.  243.  —  Magneto  Test  Set. 


FIG.  244.  —  Test  Set  Generator. 


is  accomplished  by  connecting  one  terminal  of  the  test  set  to  one 
of  the  line  wires  and  the  other  to  ground.  This  test  will  give  an 
indication  of  whether  either  line  is  grounded.  If  both  lines  test  clear, 
the  test  set  should  be  bridged  across  the  line,  to  test  for  a  cross.  In 
case  this  test  also  indicates  a  clear  line,  then  the  natural  conclusion 
is  that  the  line  is  open;  this  can  be  verified  by  attempting  to  ring 
through  to  the  next  office. 

It  may  be  well  in  this  connection  to  give  a  description  of  the  type 
of  lineman's  test  set  (Fig.  243)  best  suited  for  toll  work.  This  set 
should  be  as  light  as  possible  without  sacrificing  its  efficiency,  because 
it  must  be  readily  portable  for  long 
distances.  The  set  should  contain  a 
generator  (Fig.  244)  capable  of  ring- 
ing a  polarized  bell  through  20,000 
to  25,000  ohms  resistance,  while  the 
ringer  should  be  of  a  small  type;  an 
alternating-current  buzzer  (Fig.  245) 
has  been  used  for  this  purpose  with  good  results.  A  watchcase  re- 
ceiver, substantially  built  so  as  to  withstand  considerable  abuse, 


<->  &  * 


FIG.  245.  —  Alternating-current 
Buzzer. 


374 


TOLL  TELEPHONE  PRACTICE 


RECOVER 


GEN. 

FIG.  246.  —  Wiring  of  Lineman's 
Test  Set. 


should  be  used  for  talking  and  receiving.     The  proper  method  of 
connecting  the  apparatus  is  shown  in  Fig.  246.     When  testing,  the 

switch  rests  on  contact  a,  and  is 
switched  to  contact  b  for  talking  pur- 
poses. This  equipment,  when  placed 
in  a  small  box  and  provided  with  a 
carrying  strap,  makes  an  extremely 
light  and  compact  testing  set.  A  set 
of  this  kind  will  serve  as  the  means  of 
detecting  faults  with  quite  a  consider- 
able degree  of  accuracy,  by  noting  the 
pull  on  the  generator  and  the  sound  of 
the  bell.  On  long  toll  lines,  the  use  of 
a  test  set  becomes  unreliable,  due  to 
the  fact  that  the  large  amount  of  dis- 
tributed capacity  is  often  great  enough  to  permit'  a  flow  of  current 
sufficient  to  operate  the  bell. 

While  a  lineman's  test  set  is  of  value  in  determining  the  existence 
of  certain  troubles  on  the  line,  it  is  not  intended  that  it  should  give 
more  than  a  rough  idea  as  to  their  location.  However,  in  many  small 
toll  stations,  this  is  the  only  equipment  provided  for  making  tests, 
and  therefore  the  results  must  be  relied  upon  as  a  basis  for  trouble 
hunting.  Since  the  cost  of  electrical  testing  instruments  is  decreasing 
each  year,  and  as  there  are  some  on  the  market  to-day  that  can  be 
procured  for  a  very  nominal  figure,  no  telephone  exchange  of  any  con- 
sequence should  be  without  a  voltmeter.  The  cost  of  instruments  of 
this  class  is  as  low  as  ten  dollars  and  some  of  these  cheaper  instruments 
are  made  so  as  to  be  quite  reliable.  The  results  that  can  be  obtained 
with  them  certainly  warrant  the  investment,  to  say  the  least,  because 
they  do  so  much  to  reduce  the  cost  of  clearing  trouble.  The  higher- 
priced  portable  type  of  instrument  is  naturally  more  desirable,  but 
there  are  many  cases  in  which  their  cost  is  not  justified.  In  selecting 
a  voltmeter,  one  with  a  double  scale  should  be  chosen,  so  that  small  as 
well  as  large  voltages  may  be  accurately  measured.  One  with  a  low 
scale  of  o  to  30  and  a  high  scale  of  o  to  300  has  been  found  to  be  well 
adapted  for  general  work. 

The  voltmeter  can  be  used  not  only  for  determining  the  nature  of 
troubles,  but  also  for  locating  them,  in  many  instances.  Its  indica- 
tions are  far  more  reliable  than  those  of  a  test  set.  In  making  tests 


METHODS  OF  TESTING  375 

with  this  instrument  it  is  only  necessary  to  connect  it  in  series  with 
a  battery  and  proceed  as  in  the  case  of  a  test  set. 

The  location  of  the  trouble  may  be  found  in  some  cases  by  measur- 
ing the  resistance  of  the  line  between  the  testing  point  and  the  fault. 
Thus,  if  the  preliminary  test  indicates  a  ground,  the  resistance  of  the 
line  out  to  and  through  the  ground  can  be  obtained  in  two  general 
ways  by  means  of  a  voltmeter.  Both  of  these  methods  depend  on 
the  electrical  law  that  when  two  resistances  are  connected  in  series, 
the  fall  of  potential  in  one  is  to  the  fall  of  potential  in  the  other,  as 
the  resistance  of  the  first  is  to  the  resistance  of  the  second.  Therefore, 
to  determine  where  this  ground  exists,  the  first  step  is  to  take  a  reading 
across  the  testing  battery,  which  we  shall  call  V\  then  a  reading 
should  be  taken  with  the  voltmeter,  battery  and  defective  wire  all  in 
series,  the  first  terminal  of  the  battery  being  grounded.  Then,  if  we 
call  this  second  reading  V  ',  the  resistance  of  the  line  X  and  the  resist- 
ance of  the  voltmeter  R,  we  have,  according  to  the  law  referred  to 
above, 

V-V  :V  ::R:X 

or  V'R=X(V-V), 

which  gives  the  formula, 

'X=R\V-V'J      '    "    "    *    *    '    "     ^ 


This  method  will  give  reliable  results  only  when  the  resistance  out 
to  ground  is  rather  high,  because  of  the  fact  that  the  resistance  of  the 
voltmeter  is  usually  very  high,  running  up  to  30,000  ohms.  There- 
fore, if  the  external  resistance  is  low,  the  fall  of  potential  around  this 
resistance  will  also  be  low;  consequently  a  slight  error  in  the  reading 
of  the  instrument  will  introduce  a  much  larger  error  in  the  re- 
sult. It  is  generally  advisable  to  use  the  method  described  in  the  fol- 
lowing, because  the  line  resistance  is  seldom  high  enough  to"  insure 
good  results  with  the  first  method.  In  this  case  the  testing  battery, 
a  variable  resistance,  and  the  faulty  wire  are  all  connected  in  series 
as  before.  The  voltmeter  is  then  shunted  around  the  standard  re- 
sistance as  shown  in  Fig.  247  and  readings  are  taken  as  previously 
described.  The  variable  resistance  should  then  be  regulated  until 
the  deflection  of  the  voltmeter  is  about  one-half  of  the  battery  voltage. 
The  formula  used  with  this  method  is  the  same  as  that  derived  for  the 
first  case;  but  in  this  instance,  R  is  equal  to  the  adjusted  resistance  of 


376 


TOLL  TELEPHONE  PRACTICE 


the  variable  box  when  the  final  reading  is  taken.  To  get  the  best 
results  with  this  test,  it  is  essential  to  keep  V'  approximately  one-half 
the  value  of  V. 

After  the  resistance  of  the  wire  from  the  testing  station  to  the  fault 
has  been  obtained,  it  is  necessary  to  divide  it  by  the  resistance  per 


VOLTMETER 


LINE 


FIG.  247.  —  Voltmeter  Connections  for  Measuring  Line  Resistance. 

mile  to  obtain  the  distance.  The  resistance  per  mile  may  be  taken 
from  standard  tables;  but  the  best  method  is  to  have  on  record  the 
total  resistance  and  the  resistance  per  mile,  from  actual  measurement, 
of  each  line  leading  out  of  the  station. 

In  the  following  table  is  given  the  resistance  per  mile  for  the  various 
kinds  and  sizes  of  wire  used  in  toll-line  construction.  The  size  of  the 
iron  and  steel  wire  is  given  in  B.  W.  G.,  while  the  copper  is  given  in 
B.  &  S.  gauge;  this  is  the  general  practice  in  this  country. 

TABLE  15 

RESISTANCE  PER  MILE  OF  IRON  AND  COPPER  LINE  WIRE  AT  68 e  F. 


Iron  Wire. 

Hard- 

EBB. 

BB. 

Steel. 

Copper. 

6 

8.21 

9.6 

H-35 

2.  129 

7 

10.44 

12.21 

14-43 

2.685 

8 

12.42 

14-53 

17.18 

3.386 

9 

15-44 

18.06 

21-35 

4-277 

10 

18.83 

22.04 

26.04 

5-385 

ii 

23.48 

27.48 

32.47 

6.787 

12 

28.46 

33-3 

8.564 

13 

37-48 

43-45 

51.82 

10-794 

14 

49.08 

57-44 

67.88 

13.612 

To  determine  the  distance  to  a  cross  between  two  wires,  the  pro- 
cedure is  the  same  as  in  the  test  for  a  grounded  line;  but  instead  of 


METHODS  OF  TESTING 


377 


connecting  the  battery  to  ground,  it  is  attached  to  the  other  wire. 
The  result  obtained  by  this  test  is  the  resistance  of  the  loop,  or  the 
two  wires  in  series,  to  the  cross.  The  total  resistance  divided  by  the 
loop  resistance  per  mile  will  give  the  distance  to  the  fault. 

In  the  tests  thus  far  described,  it  is  assumed  that  the  ground  con- 
nection, or  the  cross  between  the  two  wires,  has  a  negligible  resistance. 
This  very  seldom  is  the  case,  however,  and  it  is  always  a  good  plan 
to  make  tests  from  each  end  of  a  defective  line  whenever  possible. 
Then  by  comparing  the  two  results,  a  more  reliable  conclusion  may 
be  reached. 

To  obtain  results  that  can  be  absolutely  relied  upon,  the  tests  must 
be  made  with  an  accurate  Wheatstone  bridge  of  the  form  shown  in 
Fig.  248.  The  type  of  bridge  best  suited  for  telephone  work  should 


FIG.  248.  —  Bridge. 

comply  in  general  with  the  folio  whig  specifications.  The  ratio  arms 
should  be  so  arranged  as  to  permit  of  an  adjustment  for  any  convenient 

ratio  to  each  other,  from' — to  — -,  while  the  rheostat  arm  should 

100  I 

be  so  made  that  any  resistance  from  i  to  11,000  ohms  can  be  ob- 
tained. The  galvanometer  should  be  made  a  part  of  the  set  and  should 
be  fairly  sensitive;  at  the  same  time  it  should  be  constructed  to  stand 
the  rough  usage  received  in  portable  work.  It  is  also  very  convenient 
to  have  the  battery  included  as  part  of  the  set.  A  bridge  following 
these  specifications  will  measure  any  resistance  between  i  and  100,000 
ohms,  in  which  the  error  should  not  exceed  one-quarter  of  one  per  cent. 


378 


TOLL  TELEPHONE  PRACTICE 


There  are  two  general  types  of  bridges,  one  of  which  uses  plugs  while 
the  other  makes  use  of  a  dial  rheostat.  The  plug  type  is  considered 
the  most  reliable,  although  some  telephone  companies  prefer  the 
second  because  it  is  so  easily  adjusted.  Before  attempting  to  show 
how  the  bridge  is  used  in  practice,  its  theory  will  be  given  briefly. 


FIG.  249.  —  Wire  Connectors. 

The  operation  of  the  bridge  is  based  upon  the  principle  that  the  drop 
of  potential  in  a  conductor,  when  the  current  remains  constant,  is 
proportional  to  the  resistance.  Thus,  suppose  that  V  and  V  are 
the  potentials  of  two  points  A  and  B  on  a  conductor.  Then  it  follows 
from  Ohm's  law  that 

V-  V'=RI,        .     .     .  -.     .    .     .     (2) 

in  which  R  is  the  resistance  of  that  part  of  the  conductor  on  which 
the  potential  reading  was  taken  and  /  is  the  current  flowing.  It  is 
obvious  from  this  equation  that  the  potential  difference  between  any 
two  points  on  a  conductor  in  which  a  constant  current  is  flowing,  is 
proportional  to  the  resistance  between  these  points,  provided  of  course 
that  the  conductor  is  not  the  seat  of  an  electromotive  force.  Thus 
take  a  point  X  so  situated  between  A  and  B  that  the  resistance  be- 


FIG.  250. 

tween  X  and  A  is  one-half  that  between  A  and  B,  then  the  potential 
difference  between  X  and  A  is  likewise  one-half  the  potential  between 
A  and  B. 

In  Fig.  250  is  represented  graphically  what  has  just  been  stated. 
Thus,  let  the  distances  measured  along  OG  represent  resistance  and 
those  along  OD  potentials.  It  will  then  be  evident  from  what  has 


METHODS  OF  TESTING 


379 


been  said  that  EA  equals  V  and  FB  equals  V  ';  also  that  EF  rep- 
resents the  resistance  R  between  the  points  A  and  B  on  the  con-' 
ductor.  Now,  if  we  join  points  A  and  B  and  draw  BC  parallel  to 
OG,  then  it  will  be  evident  that  AC  is  equal  to  V  -  V,  the  potential 
difference  between  A  and  B.  Therefore  the  slope  of  the  line  AB 
represents  the  rate  at  which  the  potential  drops  along  the  resistance 
R.  Then  solving  triangle  ABC,  it  is  found  that  the  tangent  of  angle 
CBA  equals 


BC~  R 


which  proves  that  the  tangent  of  the  angle  of  slope  is  equal  to  the 
strength  of  the  current.  It  will  be  noted  that  the  principle  just 
demonstrated  was  made  use  of  in  the  voltmeter  tests  previously 
described,  and  it  is  one  of  almost  universal  application  in  telephone 
testing.  The  Wheatstone  bridge  utilizes  this  principle,  the  bridge 
consisting  of  six  conductors  which  connect  four  points,  one  of  the 
conductors  contains  the  battery  and  another  the  galvanometer.  This 
is  illustrated  in  Fig.  251,  where  the  letters  Y,  Z,  S  and  T  represent 
the  four  points,  Bf  the  battery  and 
G  the  galvanometer.  Then  as  the 
fall  of  potential  between  the  points 
Y  and  5  is  the  same  by  either 
path,  YZS  or  YTS,  there  must  be 
a  point  Z  on  the  former  which 
has  the  same  potential  as  T  on 
the  latter.  Then  since  the  circuit 
through  the  galvanometer  connects 
these  two  equipotential  points,  it 


FIG.  251.  —  Wheatstone  Bridge  Circuit. 


will  receive  no  current.  Thus,  if  /  is  the  current  flowing  through  A, 
it  will  also  be  the  current  flowing  through  R,  since  none  flows  through 
the  galvanometer.  Further,  let  /'  represent  the  current  flowing 
through  the  branch  YTS.  Now,  since  the  potential  difference  be- 
tween Y  and  T  is  the  same  as  between  Y  and  Z,  we  have  by  Ohm's 
law  that 

AI=BI',      .    .    .    .    ....     (4) 

and  similarly,  RI=XIf.      ........     (5) 

And  then  by  dividing  equation  (4)  by  (5)  we  have 

AI  _  BI' 
TU~XT'    ~     R 


= 

~ 


TOLL  TELEPHONE  PRACTICE 


which  can  be  stated  in  the  proportion 

A  :R::B  :X. 


.     .     .     .     (7) 


Consequently,  when  the  four  resistances  are  so  adjusted  that  no  cur- 
rent flows  through  the  galvanometer,  the  proportion  stated  above 
always  holds.  In  practice,  three  of  the  resistances  are  fixed  and  the 
adjustment  for  a  balance  is  made  by  varying  the  fourth.  Thus,  in 
equation  (6),  X  represents  the  unknown,  while  A  and  B  represent 
the  ratio  arms  and  R  the  rheostat  or  variable  arm.  Therefore,  it  is 

ID 

only  necessary  to  know  the  ratio  — ,  for  then  the  equation  gives  the 

A 

~n 

relation  between  R  and  X,  or  X=R  —  • 

A 

In  making  a  test  to  ascertain  the  resistance  of  a  line,  the  terminals 
are  connected  to  binding  posts  marked  X  and  thus  the  line  furnishes 
the  unknown  resistance  arm  of  the  bridge.  The  test  should  be  com- 
menced with  100  ohms  in  each  of  the  ratio  arms,  and  then  the  rheostat 
arm  should  be  adjusted  until  a  balance  is  obtained,  when  the  resistance 
of  the  line  X  may  be  ascertained  by  substituting  the  proper  values 

T> 

in  the  equation  X  =  R  —  • 

A 

This  measurement  may  be  considered  as  final,  if  X  is  below  6000 
ohms;  but  if  not,  the  ratio  arms  A  and  B  should  be  readjusted  to 
conform  with  the  following  table. 

TABLE  16 


If. 

\Ti 

s  below          1.5             oh 
between       i  .  5-1  1 

It 

^ 

n-75 
78-1100 
1100-6100 

" 

f  ' 

6100-110,000 

" 

*  * 

i  io,oOo-i  ,  110,000 

BRIDGE  ARM  RATIOS 
ohms  makes  A 


i\       B  =  10,000. 


.d  =  io;      £>  =  ioo. 
.4  =  ioo;    B  —  iooo. 
.4=ioo;    .6  =  100. 
A  =1000;  5  =  ioo. 


This  table  is  given  on  the  assumption  that  a  bridge  conforming 
with  the  preceding  specifications  is  being  used. 

To  ascertain  the  resistance  of  a  wire  between  any  two  points  when 
a  second  wire  is  not  available,  the  only  method  that  can  be  followed 
is  to  connect  the  far  end  to  earth,  being  sure  that  a  good  connection 
is  made.  In  this  test  the  bridge  should  be  connected  as  shown  in 


METHODS  OF  TESTING 


381 


Fig.  252  and  a  balance  taken.  The  resistance  so  obtained,  however, 
cannot  be  relied  upon  as  being  accurate,  due  to  the  possibility  of  re- 
sistance in  the  ground  connection. 


BATT.  KEY 


LINE 


FIG.  252.  —  Wheatstone  Bridge  Connection  for  Measuring  Resistance  of  Single 

Line  Wire. 

If  three  wires  extend  between  two  toll  stations,  then  the  resistance 
of  each  wire  can  be  accurately  ascertained.  Let  X,  Y  and  Z  repre- 
sent the  respective  resistances  of  the  three  wires.  Then  if  the  far 
ends  of  any  two  are  connected  as  in  Fig.  253,  the  loop  resistance  R 
thus  obtained  will  be 

X  +  Y  =  R.    .    .    .    .    .    ...     (8) 


BATT.  KEY 


LIME,  x 


FIG.  253.  —  Bridge  Connection  for  Measuring  Line  Loop  Resistance. 

If>we  now  connect  the  far  ends  of  wires  X  and  Z  and  measure  this 
loop  in  the  same  way,  the  resistance  Rr  will  be 

X+Z=R' .    /.     (9) 

Lastly  by  connecting  the  far  ends  of  Y  and  Z,  and  letting  the  re- 
sistance of  this  loop  equal  R",  the  result  will  be 

Y+Z=R" (10) 

With  these  three  equations  (8),  (9)  and  (10),  the  values  of  X,   Y 
and  Z  can  be  found  as  follows. 


382  TOLL  TELEPHONE  PRACTICE 

First,  subtract  equation  (10)  from  (9), 

X-  Y=R'-  R",      ......     (n) 

then  add  (n)  to  (8)  and  eliminate  F,  or 

2X=R  +  R'-R", 

i  •  "i    •  IT-    R  ~f~  R  —  R  /    \ 

which  gives  X  =  -  .    .     .    .    .    .    .    .    (12) 

Similarly   Y  and  Z  can  be  found;  and 


Z-*  +  *'-*.      .     .    ,.  (14) 

If  there  are  but  two  wires  between  the  stations,  the  ground  can  be 
used  as  the  third  conductor,  and  then  the  procedure  is  the  same  as 
described  above  for  three  wires.  First  make  the  measurement  of  the 
two  wires  in  series,  next  of  each  one  connected  to  ground,  and  then 
the  calculations  will  follow,  as  in  the  preceding  paragraph.  The 
ground  return  resistance  should  be  very  small,  measuring  not  more 
than  ten  ohms  if  proper  earth  connections  are  made. 

In  the  method  just  described,  trouble  may  be  encountered  in  the 
form  of  earth  potentials,  and  this  is  especially  true  if  the  line  parallels 
an  electric  railway.  Where  the  earth  potentials  are  smaller  than  the 
testing  voltage  and  relatively  steady,  an  additional  measurement 
should  be  made  in  each  case  with  the  terminals  of  the  battery  reversed, 
and  a  mean  of  the  two  results  should  be  used  in  the  calculations. 
Earth  currents  may  be  readily  detected  by  a  milliammeter  connected 
between  one  end  of  the  line  and  ground,  when  the  far  end  is  also 
grounded. 

The  most  important  use  made  of  the  bridge  is  the  location  of  such 
faults  as  grounds  and  crosses.  The  accurate  location  of  these  faults 
is  extremely  essential,  so  that  proper  directions  may  be  given  to  the 
linemen  to  clear  the  trouble  with  as  little  delay  to  the  service  as 
possible. 

When  the  trouble  consists  of  a  simple  ground  and  a  second  wire  is 
available,  the  location  of  the  fault  is  comparatively  easy.  The  pro- 
cedure in  this  case  is  known  as  the  Varley  loop  test.  In  making  this 
test,  the  first  step  is  to  connect  the  far  end  of  the  faulty  wire  to  its 


METHODS  OF  TESTING 


383 


mate,  or  any  other  clear  wire,  and  measure  the  loop  with  the  connec- 
tions set  up  as  shown  in  Fig.  254.  Then  if  the  loop  resistance  b£ 
represented  by  R,  we  have 

R=X+Y.       .......    (15) 


BATTKET 


FIG.  254.  —  Connection  for  First  Measurement  in  Varley  Loop  Test. 

Now,  without  changing  the  line  connections  on  the  bridge,  one 
terminal  of  the  battery  should  be  switched  to  ground,  as  shown  in 
Fig.  255,  and  another  balance  obtained;  the  following  conditions  will 
then  exist. 

A  _ 

B 


(16) 


FIG.  255.  —  Connection  for  Second  Measurement  in  Varley  Loop  Test. 

By  substituting  in  (16)  the  value  of  Y  obtained  from  (15), 

A      r'+X 


B      R-X' 


and  clearing  of  fractions, 

AR-AX=Br'+BX, 

AX+BX  =  AR-Br1 

AR-Br' 

A+B    '    *     • 


or 

which  gives 


(18) 


384  TOLL  TELEPHONE  PRACTICE 

In  the  above  equations  r'  is  the  resistance  of  the  rheostat  arm.  One 
more  test  is  usually  made  before  the  result  is  accepted,  merely  to  serve 
as  a  check.  The  connections  are  the  same  as  shown  in  Fig.  255,  but 
with  the  line  connections  reversed  at  D  and  E.  Now  if  R'  and  r"  are 
the  resistances  of  the  bridge  arms  used  to  reach  a  balance,  then 

A      r"  +  Yf 


Substituting  for  Yf  in  the  terms  of  X', 

A  _r"+R'-X' 
B  X' 

and  clearing  of  fractions, 

AX'  +  BX'  =  Br"  +  BR'. 
Then  solving  for  X', 

*-*&?  ........  >> 

The  average  of  the  results  obtained  in  these  two  tests  will  give  a 
more  accurate  location  than  either  one  alone;  but  one  result  should 
check  the  other  very  closely  if  the  measurements  have  been  made 
with  due  care.  To  obtain  the  distance  to  the  fault,  divide  the  result 
thus  obtained  by  the  resistance  per  mile  of  the  faulty  conductor. 

Another  method  of  obtaining  the  same  results,  known  as  the  Murray 
loop  test,  can  be  used  to  advantage  either  as  a  check  on  the  preceding 
method  or  for  direct  location.  Here,  as  in  the  previous  test,  the  far 
end  of  the  faulty  wire  is  connected  to  a  good  wire  and  the  loop  meas- 
ured, giving  the  resistance 

R  =  X  +  7. 

The  bridge  is  then  connected  as  shown  in  Fig.  256,  and  it  will  be 
noted  that  in  this  case  there  are  only  two  adjustable  arms,  since  A 
and  r  now  constitute  a  single  arm.  X  and  Y  constitute  the  other  two 
arms  of  the  bridge,  with  the  ground  as  the  junction.  If  a  balance  is 
now  obtained, 

A+/      Y 


x >  •  <»> 


And  by  substituting  R-  X  for  F, 


T7-  BR  f          X 

X=A+r'+B (22) 


METHODS  OF  TESTING 


385 


This  result  may  be  checked  by  reversing  the  line  wires  as  in  the 
Varley  test.  Some  bridges  are  not  arranged  for  switching  the  galva- 
nometer terminal  to  the  point  D  for  making  this  kind  of  test ;  but  the 
standard  forms  that  are  made  expressly  for  telephone  work  are  usually 
so  constructed.  In  case  a  bridge  is  not  available,  or  the  one  at  hand 


FIG.  256.  —  Connection  for  Second  Measurement  in  Murray  Loop  Test. 

is  not  arranged  so  that  this  change  in  the  connections  can  be  made, 
the  test  may  still  be  accomplished  if  two  adjustable  resistance  boxes 
can  be  procured  and  the  loop  resistance  is  known.  In  this  event  it  is 
necessary  only  to  substitute  the  resistance  boxes  for  the  two  arms, 
while  any  galvanometer  or  a  sensitive  telephone  receiver  may  be  used 
in  place  of  the  instrument  usually  mounted  in  the  bridge.  The  con- 
nections should  be  set  up  as  shown  in  Fig.  257,  and  it  will  be  noted 
that  they  are  the  equivalent  of  those  in  Fig.  256. 


FIG.  257.  —  Murray  Loop  Test,  Using  Resistance  Boxes. 

In  both  the  Murray  and  the  Varley  loop  tests,  the  resistance  of  the 
fault  and  the  presence  of  earth  currents  have  no  effect  on  the  accuracy 
of  the  results.  The  reason  for  this  is  found  in  the  fact  that  the  re- 
sistance of  the  fault  lies  outside  of  the  neutral  point  G  and  forms  part 


386  TOLL  TELEPHONE  PRACTICE 

of  the  battery  circuit.  It  might  be  well  to  add  that  in  case  con- 
siderable resistance  is  introduced  by  the  leads  used  in  connecting  the 
line  wires  to  the  bridge,  it  should  be  deducted  from  the  value  of  X 
before  computing  the  distance  to  the  fault.  However,  in  most  cases 
this  resistance  is  so  small  as  to  be  negligible. 

When  no  clear  wire  is  available  for  making  a  loop  test,  the  following 
method  may  be  used  with  a  high  degree  of  accuracy,  in  case  the  re- 
sistance of  the  fault  is  constant.  For  this  test  the  bridge  should  be 
connected  as  shown  in  Fig.  258  and  the  usual  balance  obtained.  The 
result  thus  obtained  is  the  resistance  of  X  +  Z.  Let  this  be  repre- 
sented by 

R'=X+Z.      .    ,     .    >    .-   .,  .     (23) 


FIG.  258.  —  Connection  for  Measurement  When  Resistance  of  Fault  is  Constant. 

Then  the  same  test  from  the  opposite  end  of  the  line  should  be  made 

giving 

R»=  Y+Z.       .......     .     (24) 

The  total  resistance  of  the  line  —  either  previously  determined  or 
computed  from  its  size,  length  and  temperature  —  may  be  represented 

by 

R=X  +  Y.       .......     (25) 

Then  by  subtracting  equation  (24)  from  (23), 

#'-  R"  =  X-  Y.      .  -..     .     ..    .     .     (26) 

Then  substituting  the  value  of  Y  =  R  —  X,  and  solving  for  X, 

x=R±RL-^_  .   .   .    (27) 

2 

Now  since  the  resistance  to  the  fault  and  the  resistance  per  mile  of 
wire  are  known,  it  is  an  easy  matter  to  determine  the  location. 

In  making  tests  for  the  location  of  crosses,  the  procedure  is  similar 
to  that  already  given  for  the  location  of  grounds.  In  the  first  place, 


METHODS   OF  TESTING 


387 


it  is  not  always  safe  to  assume  that  the  resistance  of  the  fault  is  negli- 
gible, although  it  may  be  so  in  many  instances.  It  is  safer  to  assume 
that  the  fault  has  a  perceptible  resistance  and  make  all  tests  accord- 
ingly. All  such  tests  for  location  of  crosses  require  two  measurements, 
or  more.  The  Varley  loop  method  is  one  of  the  simplest  and  best, 


BATT.  KEY 


FIG.  259.  —  First  Connection  in  Varley  Loop  Measurement  for  Crosses. 

and  the  results  obtained  can  be  relied  upon  where  the  resistance  of 
the  fault  is  constant.  In  making  this  test  the  bridge  connections 
should  be  set  up  as  shown  in  Fig.  259,  and  the  resistance  of  the  loop 
measured.  Let  the  resistance  be  called  R.  Then 


R=  x+  Y+Z. 


(28) 


FIG.  260.  —  Second  Connection  in  Varley  Loop  Measurement  for  Crosses. 

Either  of  the  crossed  wires  is  next  connected  to  ground  at  any  point 
beyond  the  fault.  This  is  readily  accomplished  at  the  next  toll  station, 
and  the  bridge  is  then  connected  as  shown  in  Fig.  260.  It  follows 
from  the  second  balance  that 

A      r+X 


Then  from  equation  (28), 


Y+Z  =  R-  X 


(29) 


(30) 


388 


TOLL  TELEPHONE  PRACTICE 


Substituting  this  value  for  (  F  +  Z)  in  (29), 

A       r+X 

B      R-X'      ' 


and  by  clearing  of  fractions  and  solving  for  X, 

AR-  Br 


X 


A  +B 


(32) 


and  by  dividing  by  the  resistance  per  mile  of  wire,  the  distance  to  the 
fault  is  obtained.  This  test  may  be  checked  by  reversing  the  two 
wires  at  D  and  E,  or  by  placing  the  ground  H  on  the  other  wire. 

It  is  sometimes  advisable  to  check  the  result  by  a  different  method, 
if  possible.  The  following  test  can  be  used  in  some  instances.  The 
first  measurement  is  made  as  in  the  preceding  test,  while  the  second 
is  made  with  the  connections  shown  in  Fig.  261.  This  determines 
the  resistance  of  the  wire  ES,  which  will  be  termed  Rf.  Then 

R'  =  X  +  W.  (33) 


BATT.  KEY 


FIG.   261.  —  Second   Connection  in  Varley  Loop    Test    for   Locating   High-resistance 

Crosses. 

Next  disconnect  the  wire  ES  from  the  bridge  and  substitute  UV, 
thus  measuring  the  resistance  of  the  portion  between  the  testing 
station  and  the  fault,  the  fault  itself  and  the  part  ES  beyond  the  fault 
all  in  series.  Let  this  resistance  be  denoted  by  R".  Then 

R»  =  Y  +Z  +  W 

Next  adding  equations  (28)  and  (33), 

R  +  R'  =  2  X  +  Y  +  Z  +  W,  .     .     .     . 
and  by  subtracting  (34)  from  (35), 

R  +  R'  -  R" 


(34) 


(35) 


(36) 


METHODS  OF  TESTING 


389 


This  is  the  resistance  of  the  wire  from  the  bridge  to  the  fault;  the 
distance  being  obtained  as  already  explained  in  the  other  cases.  TJiis 
test,  like  the  previous  one,  is  reliable  only  when  the  resistance  of  the 
fault  is  constant. 

Difficulty  in  keeping  the  bridge  balanced  during  a  test  may  be 
caused  by  varying  resistance  at  the  fault.  The  following  test  will 
sometimes  obviate  this  difficulty.  The  first  measurement  is  made 
with  the  bridge  connected  as  shown  in  Fig.  261.  Then 

R=  X  +  W.     .......    (37) 

The  bridge  should  then  be  connected  as  indicated  in  Fig.  262,  from 
which  it  will  be  observed  that  the  three  arms  have  been  reconnected 
to  form  but  two,  namely,  B  and  A  +  r.  The  galvanometer  is  not 


FIG.  262.  —  Connection  for  Second  Measurement  of  Variable-resistance  Crosses. 

connected  directly  across  the  arms  in  the  bridge,  but  through  Y  and 
Z  to  the  point  F,  which  forms  the  junction  of  X  and  W.  The  other 
two  arms  of  the  combination  are  furnished  by  the  resistances  X  and 
W.  Now,  since  the  resistance  Z  is  in  the  galvanometer  circuit,  it 
need  not  be  constant,  because  no  current  will  flow  through  it  when  a 
balance  is  obtained.  Then 

A+r  _X 
B         W      •••••• 


(38) 


and  by  substituting  the  value  of  W  as  obtained  from  (37),  and  solving, 

....  (39) 


(A±r)_R 
~  A+B+r' 


This  is  the  resistance  to  the  fault,  from  which  the  distance  is  obtained 
in  the  usual  manner.  In  order  to  get  a  close  balance,  where  Y  and  Z 
are  of  considerable  resistance,  it  is  sometimes  necessary  to  use  a  higher 
voltage  than  usual. 


390 


TOLL  TELEPHONE  PRACTICE 


In  the  tests  described  thus  far,  nothing  has  been  said  regarding  the 
location  of  open  conductors  or  breaks.  In  describing  the  tests  for 
this  purpose,  only  those  faults  in  which  the  broken  ends  are  insulated 
from  the  ground  or  other  wires  will  be  considered,  as  all  others  can 
be  located  by  the  methods  already  given.  Faults  of  this  class  cannot 
be  located  as  a  whole  with  the  same  accuracy  as  grounds  or  crosses; 
but  the  usual  limits  of  accuracy  are  sufficient  for  lines  in  cable,  and 
of  some  help  in  the  case  of  open  wires. 

The  theory  is  briefly  as  follows:  Referring  to  Fig.  263,  let  the 
potential  of  point  E  be  represented  by  Fi,  and  that  of  H  by  F3. 

Then  when  a  balance  is  reached, 
i.e.,  when  no  current  flows  through 
the  galvanometer  on  the  make  and 
break  of  the  battery  key,  the  poten- 
tial of  points  D  and  F  must  be 
equal,  and  may  be  represented  by 
F2.  Therefore,  if  Qi  and  ()2  rep- 
resent the  quantities  of  electricity 
flowing  into  the  condensers  of  ca- 

FIG.  263.  — Theoretical  Connection  for     pacities  Ci   and  C2,  through  the  re- 
Capacity  Test,  sistances  A  and  B,  respectively,  it 
follows,  since  Ci  and  C2  are  charged  to  the  same  potential  ( F3  —  F2) , 
that 

ft=Ci(7,-Fs)  .    .    .(  .    .    .    .     (40) 
and 

ft  -  C,  (K,  -  70 -..',    (41) 


BATT.  KEY 


Dividing  equation  (40)  by  (41)  we  have 

Qi  =Ci 

ft      C2* 


(42) 


But  when  a  condenser  is  charged  through  a  resistance  from  a  source 
of  constant  E.M.F.,  or  when  it  is  afterward  discharged  through  a 
resistance,  the  instantaneous  value  of  the  current  flowing  is 


•       Q     -X 
= 


(43) 


where  Q  is  the  final  charge,  or  the  initial  charge,  as  the  case  may  be, 
and  R  is  the  resistance,  C  the  capacity  and  /  the  time  from  the  moment 


METHODS  OF  TESTING 


391 


of  commencing  the  charge  or  discharge.     But  Q  =  CE  and  so  (43) 
becomes 


E   __L 

- 


(44) 


and  the  fall  of  potential  through  the  resistance  at  any  instant  is 

Ri  =  E€~JC.      .     .     .     .     .     .     .     (45) 

But  in  Fig.  263,  if  no  current  flows  through  the  galvanometer,  the 
potentials  (V\  —  F2),  or  the  drop  through  A  and  B  respectively, 
must  be  alike  at  any  instant.  But  it  is  evident  that  such  equality, 
referring  to  (45),  depends  upon  the  exponential  term  and  RC  must  be 
the  same  in  each  case.  Therefore 

.  .  .--;  .  .  .  (46) 

or  ~  =^T,     .......  ' .    (47) 


£1  =# 

C2  ==  A  ' 


which  supplies  the  means  of  comparing  one  capacity  with  another,  or 
with  a  known  standard. 

Now  if  it  is  desired  to  locate  a  break  in  a  wire,  the  bridge  should  be 
connected  as  shown  in  Fig.  264.  A  and  B  in  this  figure  represent  the 
two  resistance  arms  shown  in  Fig.  262,  and  at  least  one  of  these  must 
be  adjusted  in  order  to  obtain  a  balance.  If  desired,  two  resistance 
boxes  may  be  used  in  place  of  the  bridge.  Then  with  the  connections 
set  up  as  shown  in  the  circuit,  Fig.  264,  the  far  end  of  the  faulty  wire 


FIG.  264.  —  Connection  for  Locating  Break  in  Line  Wire  by  Capacity  Test. 

should  be  connected  to  a  good  wire  of  the  same  size,  and  the  resistances 
A  and  B  adjusted  so  that  when  the  key  K  is  operated  and  released, 
the  galvanometer  needle  will  not  be  deflected.  A  balance  of  this 
kind  will  indicate  that  the  potentials  at  D  and  E  are  equal.  In  this 


392  TOLL  TELEPHONE  PRACTICE 

test  the  line  wire  DF  forms  one  plate  of  the  condenser  and  the  earth 
the  other,  while  the  wire  EGF  is  one  plate  and  the  earth  the  other  of 
the  second  condenser.  Then  since  the  capacity  of  a  wire  is  propor- 
tional to  its  length, 

A  _^Y  +  W 

B=       X     ' 
and  since 

W  =  F  -  X, 
then 

2  BY 


X  = 


A+B' 


in  which  X  and  F  may  be  expressed  in  miles  or  feet  as  desired.  Then 
if  the  length  of  the  wire  Y  be  substituted  in  the  above  formula,  one 
will  have  the  distance  to  the  fault  in  feet  or  miles  according  to  the 
units  substituted. 

In  making  the  above  test,  it  may  be  convenient  to  use  a  telephone 
receiver  in  the  place  of  the  galvanometer,  and  a  high-frequency  inter- 
rupter instead  of  the  key;  before  a  balance  is  reached,  sufficient  current 
will  flow  through  the  receiver  to  produce  an  audible  sound. 

The  measurement  of  insulation  resistance  at  periodic  intervals  is 
very  essential  in  proper  maintenance  of  toll  lines.  The  voltmeter 
method  is  simple  and  rapid,  and  very  generally  used.  It  requires 
simply  a  battery,  of  perhaps  100  cells,  and  a  voltmeter.  Let  E  be 
the  battery  voltage,  V  the  reading  of  the  voltmeter,  r  the  resistance 
of  the  voltmeter  and  /  the  length  of  the  line,  when  the  voltmeter  is 
connected  in  series  with  the  battery  to  line,  the  far  end  being  open, 
and  the  other  side  of  the  battery  grounded.  Then  the  insulation 
resistance  in  ohms,  per  mile  of  line,  is 


R=lr 


(i-) 


s  This  method  is  quite  satisfactory  unless  the  line  is  very  long  or 
the  insulation  resistance  is  very  low,  or  both.  For  such  cases  a  method 
has  been  given  by  Mr.  F.  F.  Fowle,1  which  requires  the  same  appa- 
ratus, but  one  additional  reading.  The  first  reading  is  taken  as 
before,  with  the  far  end  of  the  line  open.  The  second  reading  is 
taken  with  the  same  connections,  except  that  the  far  end  of  the  line 
is  connected  directly  to  ground.  Let  the  second  reading  of  the  volt- 

1  "The  Measurement  of  Distributed  Leakage  on  Transmission  Lines";  Electrical 
World,  Feb.  6,  1904. 


METHODS   OF  TESTING 


393 


meter  be  V  and  in  this  case  let  /  be  the  line  resistance  per  mile. 
Then  the  true  insulation  resistance  per  mile  is 


This  method  should  be  used  when  the  insulation  is  low,  if  accurate 

'results  are  desired.     In  many  cases  the  voltmeter  readings  will  not 

be  alike  if  the  battery  is  reversed  and  a  check  reading  taken;  in  such 

cases  the  average  reading  should  be  used,  and  as  a  rule  this  procedure 

should  be  followed. 

In  dry  clear  weather  a  line  in  good  physical  condition  ought  to 
measure  at  least  ten  megohms  per  mile,  but  during  a  heavy  rainfall 
it  may  diminish  to  a  fraction  of  a  megohm  per  mile.  The  minimum 
value  depends  on  the  type  of  insulator  employed,  the  number  per  mile 
and  the  amount  of  dirt  and  soot  normally  present  in  the  atmosphere. 
An  average  minimum  of  one-quarter  of  a  megohm  per  mile  is  as  low 
as  the  insulation  ought  to  fall  and  a  higher  value  should  be  obtained 
if  possible.  Careful  attention  to  maintenance  is  most  essential  in 
securing  high  insulation,  especially  in  the  matter  of  trimming  foliage 
and  replacing  broken  insulators. 

Regarding  the  last  classification  of  troubles,  i.e.,  foreign  currents, 
as  given  in  the  table,  these  can  sometimes  be  detected  by  bridging  a 
suitable  current  detector  across  the  line,  or  from  each  line  wire  to 
ground,  on  which  this  trouble  exists.  If  the  trouble  arises  from  a 
cross  with  a  direct-current  source,  it  can  be  easily  verified  by  means 
of  a  direct-current  voltmeter,  or  an  alternating-current  instrument 
when  the  source  is  alternating.  The  only  method  of  locating  this 
trouble,  after  it  has  been  positively  identified,  is  to  inspect  the  line. 
In  the  case  of  induced  currents  from  foreign  sources,  the  best  remedy 
is  always  to  relocate  the  telephone  line  beyond  the  zone  of  influence. 
This  is  not  always  necessary,  however,  and  the  usual  remedies  have 
been  discussed  in  Chapter  XIX. 

It  should  be  noted  that  loaded  circuits  contain  an  additional  element 
which  must  be  considered  in  all  resistance  measurements.  Each 
loading  coil  introduces  in  the  circuit  a  certain  definite  resistance, 
usually  1.25  ohms,  and  unless  this  is  accounted  for  in  the  final  cal- 
culation, the  result  will  be  in  error.  It  is  necessary  to  determine, 
from  the  known  spacing  of  the  coils,  how  much  resistance  each  coil 
adds  per  mile  of  wire,  which  should  be  added  to  the  wire  resistance 
per  mile. 


CHAPTER  XXI 
TOLL-LINE  MAINTENANCE 

THE  design  and  initial  installation  of  a  toll  line  is  a  problem  that 
requires  a  high  class  of  engineering  skill.  Likewise,  the  task  of  keep- 
ing the  line  in  good  working  condition  after  it  has  been  completed  is 
an  undertaking  that  requires  not  only  reasoning  ability  and  careful 
observation,  but  also  a  knowledge  of  working  conditions,  which  can 
be  attained  only  by  practical  experience.  The  importance  of  main- 
tenance in  its  relation  to  good  service  can  hardly  be  underestimated. 
The  form  of  organization  required  is  simple,  but  essential.  The 
lines  are  divided  into  sections  and  one  or  more  sections  assigned  to  a 
resident  lineman,  who  is  made  responsible  for  the  condition  of  his 
territory.  His  work  consists  of  clearing  line  trouble  and  making  all 
ordinary  repairs;  he  is  also  required  to  make  periodical  inspections, 
which  ought  not  to  be  more  than  three  months  apart.  The  linemen 
are  ordinarily  under  the  authority  of  the  wire  chief,  who  directs  all 
of  their  work. 

In  order  that  the  maintenance  may  be  systematized,  each  wire  chief 
should  be  provided  with  a  complete  record  of  every  line  in  his  territory. 
This  record  should  cover  the  kind  and  gauge  of  the  wire,  the  pin 
number,  test  poles  and  test  stations  to  the  limits  of  the  territory. 
There  are  various  methods  of  keeping  such  records.  One  of  the  most 
satisfactory,  where  many  lines  are  to  be  considered,  is  by  means  of 
card  files.  In  this  case,  a  card  file  is  prepared  for  each  route,  giving 
the  position  of  each  wire  on  every  pole  and  the  corresponding  jacks 
^at  the  test  stations.  While  this  appears  cumbersome  at  first  sight, 
it  is  not  so  in  fact  and  the  value  of  the  record  amply  repays  its  cost. 
The  first  essential  is  a  printed  card,  showing  the  requisite  number  — 
or  better,  the  ultimate  number  —  of  cross-arms,  with  sufficient  room 
for  making  any  desired  notations.  In  Fig.  265  is  shown  such  a  card 
for  a  four-arm  pole  line.  It  will  be  noted  that  all  the  information 
needed  by  the  wire  chief  is  given,  including  the  circuit  number,  pin 
number  and  the  gauge  and  resistance  of  the  wire  from  the  wire  chief's 

394 


TOLL-LINE  MAINTENANCE 


395 


test  board  to  the  pole  in  question.  A  card  of  this  kind  is  filled  out 
for  each  pole  at  which  any  change  in  the  arrangement  of  the  wires 
takes  place.  For  example,  suppose  that  one  card  shows  pole  No. 
13,340  and  the  next  card  in  the  file  is  13,373.  This  would  indicate 


TEST  TOLL 
EASTON*! 

BENTON-  EASTON 
ROUTE 

EASTON'Z            CLINTON  *i             EASTON  *3 

POLE    14571 
JEFFERSON*! 

01  0 

o;::  o 

ol2_c  o   Q&Q 

o^o 

1 

JEFFERSON*? 

HIXTON*! 

BOLTON*!                    BARNET*! 

BOLTON  \ 

o^o 

o;;:c  o 

cC  o    o;~o 

o«*"o 

GRAFF*! 

A5HLANP*! 

A5HLANP*2                AUBURN* 

AUBURN^ 

0"°  0 

oioTo 

0£   0     Oro 

O"c  O 

HOWE.*! 

HUM  BOLT  *l 

HOWE  *Z                    LENOX*! 

FAU5CITY*! 

cC  o 

o^  o 

cC"  o    o^.7o 

o1007^ 

FIG.  265.  —  Form  of  Pole-line  Record. 


TEST    PANEL- 
HILTON     STATION 


fOLE.     I-1-527 


BENTON    EA5TON    ROUTE 


£      *§     •" 

1  i  i 

UJ        O         uj 


&        *      %        Z        H        Z 

i  I  !  I  I  1 

"5          ~>          X          CQ          OQ          (Q 


oooooooooooooooooooo 

cJ^vp<o95JlfiS^ 

o~o  ob  d°o  ONO  o^o  o"o  o~o  o"o  o"o  oco 


FIG.  266.  —  Form  of  Test-panel  Record. 

that  all  intervening  poles  are  duplicates  of  No.  13,340  in  so  far  as  the 
arrangement  of  the  line  wires  is  concerned,  and  that  at  pole  No.  13,373, 
some  change  has  taken  place  which  can  be  readily  observed  by  com- 
paring the  cards.  In  Fig.  266  is  shown  a  card  which  indicates  a  method 


396  TOLL  TELEPHONE  PRACTICE 

of  keeping  test  panel  records.  These  cards  should  be  filed  in  their 
proper  places,  according  to  location,  among  the  pole-line  cards. 

When  a  record  of  each  route  is  kept  in  the  above  form,  the  wire 
chief  has  at  hand  all  of  the  desired  information  pertaining  to  any  line ; 
and  consequently,  when  a  lineman  calls  in  and  reports  that  he  is  at 
a  certain  pole  number,  the  wire  chief  can  immediately  turn  to  the 
card  for  this  particular  pole  and  obtain  any  necessary  information. 
Each  lineman's  station  should  be  provided  with  a  test  panel,  of  the 
type  described  fully  in  Chapter  XVI.  This  panel  should  be  located 
as  near  the  center  of  the  section  as  convenient,  and  is  often  placed  in 
the  local  exchange,  or  sometimes  in  the  lineman's  home. 

The  location  and  number  of  these  testing  stations  on  a  toll  route 
depends,  for  the  most  part,  on  physical  and  climatic  conditions.  For 
example,  in  the  southwestern  part  of  the  country  where  the  climate 
is  dry  and  warm  throughout  the  entire  year  and  storms  are  of  infre- 
quent occurrence,  the  facilities  for  testing  need  not  be  very  elaborate. 
The  testing  stations  can  be  safely  located  at  long  intervals  and  line- 
men's sections  can  correspond.  In  regions  such  as  the  middle  and 
northern  states,  where  opposite  conditions  prevail,  the  testing  stations 
must  be  located  correspondingly  closer  together.  Under  the  latter 
conditions,  maintenance  is  more  difficult,  particularly  in  mountainous 
regions.  Under  average  conditions,  each  lineman's  section  should  be 
about  75  to  100  miles  long,  with  the  station  as  near  the  center  as 
possible,  in  order  to  minimize  the  distance  traveled  in  clearing  trouble. 
The  transportation  facilities  naturally  play  an  important  part  in 
determining  the  sections. 


FIG.  267.  —  Test-panel  Wiring. 

The  method  of  wiring  the  lines  through  the  test  panels  is  shown  in 
Fig.  267.  The  panels  should  be  so  located  that  as  little  wire  as  possible 
will  be  needed  in  looping  the  lines  through  them.  In  making  the 
connections  from  the  line  to  the  jacks,  rubber-covered  cable  or  a  good 
grade  of  twisted  pair  wire,  whose  gauge  is  not  smaller  than  No.  16 


TOLL-LINE  MAINTENANCE 


397 


B.  &  S.,  should  be  used.  The  lines,  both  "  in  "  and  "  out/'  should 
pass  through  suitable  fuses,  preferably  of  the  tubular  type,  and  car- 
bon block  arresters.  Each  test  station  should  be  provided  with*  a 
standard  telephone  set,  normally  connected  to  some  particular  line 
by  means  of  a  key  or  a  double-pole,  double-throw  knife  switch.  The 
method  of  wiring  this  equipment  is  given  in  Fig.  268.  This  shows 
the  key  in  its  normal  position  with  the  telephone  set  connected  to  the 
line.  It  will  be  noted,  however,  that  by  throwing  the  key  to  the 
opposite  position,  the  twin  plug  will  be  connected  to  the  set,  which 


FIG.  268.  —  Wiring  of  Lineman's  Telephone  Set  at  Test  Station. 

permits  connection  with  any  line  in  the  panel.  The  lineman's  set 
is  normally  connected  to  a  toll  line,  which  is  in  service;  in  order  that 
the  wire  chief  may  call  him,  a  code  signal  is  prearranged. 

The  test  station  should  also  be  provided  with  patching  cords,  plugs 
and  a  ground  connection  for  making  the  usual  simple  tests  and  for 
patching  lines  in  emergencies.  Each  of  the  patching  cords  consists 
of  a  short  cord  with  a  single-conductor  plug  attached  to  each  end,  and 
is  used  to  make  up  clear  circuits  when  part  of  the  lines  are  in  trouble. 
For  instance,  all  the  circuits  between  two  particular  points  might  be 
in  trouble,  while  it  would  still  be  possible  to  make  up  a  through  circuit 
by  patching  the  clear  portions  together  at  the  test  stations.  This  is 
always  done,  if  possible,  in  the  case  of  general  trouble;  the  patches  are 
always  made  under  the  order  of  the  wire  chief.  The  diagram  in 
Fig.  269  gives  a  concrete  example  of  what  may  be  accomplished  by 
patching.  The  crosses  in  the  figure  represent  the  locations  of  the 
faults;  the  rectangles  A  and  F  at  each  end  represent  the  toll  stations 
at  which  wire-chief's  test  boards  are  located,  and  the  rectangles 


398 


TOLL  TELEPHONE  PRACTICE 


B-C-D-E,  the  linemen's  test  stations.  It  will  be  observed  that  five 
out  of  six  lines  are  in  trouble  at  different  points  between  A  and  F, 
but  by  means  of  patches  at  the  several  linemen's  stations,  all  except 
one  of  the  lines  are  made  serviceable. 

In  case  the  lines  are  operated  on  a  simplex  or  composite  basis,  a 
morse  schedule  or  layout,  with  which  each  lineman  should  be  thor- 
oughly familiar,  must  be  maintained.  This  schedule  gives  the  hours 
and  circuits  used  for  these  purposes,  so  that  the  lineman  will  not  cut 
in  with  his  telephone  or  open  any  of  these  circuits  at  the  test  panel,  as 


1 

2 

3 

V 

/ 

-- 

1 

2 
3 

y 

J 

^ 

4 

r 

} 

y 

/ 

/ 

5 

X 

FIG.  269.  —  Illustration  of  the  Use  of  Patches. 

this  would  open  the  morse.  This  schedule  should  read,  for  example, 
as  follows:  i  and  2  are  composited;  3  and  4,  5  and  6  are  phantomed; 
7  and  8  are  simplexed;  9  and  10  are  straight,  etc.  The  lineman  should 
be  acquainted  with  the  hours  during  which  this  service  is  maintained. 
The  duties  of  a  lineman  are  more  than  those  of  a  mere  trouble- 
hunter,  a  fact  that  may  well  be  emphasized.  He  ought  to  inspect 
his  line  periodically  and  at  every  available  opportunity,  making  all 
light  repairs  as  he  proceeds;  there  are  frequent  opportunities  for  this 
in  connection  with  his  trips  to  clear  line  troubles.  The  replacing  of 
occasional  poles  is  work  which  he  can  readily  handle  with  a  few  men 
hired  as  needed.  He  can  also  replace  the  cross-arms,  when  such 
general  replacement  becomes  necessary.  The  heavy  replacement 
work  on  the  pole  line  itself  is  usually  assigned  to  the  construction 
department. 

\  The  company's  right-of-way  privileges  should  also  be  thoroughly 
understood  by  the  lineman,  so  that  he  may  be  governed  accordingly 
in  his  relations  with  the  owners  of  abutting  property.  This  applies 
often  to  the  matter  of  trimming  rights.  The  lineman  may  act  in  the 
capacity  of  a  right-of-way  agent  in  minor  matters. 


CHAPTER  XXII 
THE  TELEPHONE  REPEATER 

TELEPHONE  currents  in  long-toll  circuits  become  very  much  attenu- 
ated by  the  effects  of  resistance,  leakage  and  capacity,  as  already 
shown.  The  rate  of  attenuation  can  be  reduced  materially  by  means 
of  artificial  inductance  loading,  but  even  this  is  expensive,  compara- 
tively, so  that  a  device  for  relaying  these  weak  currents  and  increasing 
their  energy  is  very  desirable  if  it  can  be  obtained.  There  has  existed 
a  demand  for  a  successful  two-way  telephone  relay  or  repeater  ever 
since  the  advent  of  long-distance  telephony  and,  as  a  consequence, 
the  experimental  and  research  work  in  this  field  has  been  incessant. 
The  various  ideas  and  schemes  that  have  been  developed  are  so  numer- 
ous that  a  description  of  all,  or  even  a  few  of  them,  is  beyond  the 
present  scope.  Then  again,  but  one  of  all  of  these  devices  is  used 
commercially,  so  that  the  study  of  the  others  possesses  only  a  scientific 
interest  and  would  be  of  value  merely  in  tracing  the  gradual  evolu- 
tion from  the  simple  one-way  experimental  repeater  to  the  practical 
Shreeve  two-way  repeater  now  in  use. 

The  steps  in  this  evolution  may  be  readily  outlined,  however,  with- 
out giving  a  detailed  description  or  making  direct  reference  to  the 
many  experimental  repeaters  that  have  been  tried.  It  is  in  this 
manner  that  the  development  will  be  briefly  traced,  in  order  to  bring 
out  some  of  the  peculiar  and  interesting  difficulties  encountered. 

The  first  attempts  in  the  construction  of  a  telephone  repeater  were 
guided,  in  a  measure,  by  what  seems  an  analogous  case,  the  telegraph 
repeater.  This,  however,  was  a  fallacious  conception,  inasmuch  as 
the  telegraph  repeater  responds  merely  to  single  impulses;  whereas  a 
telephone  repeater  must  reproduce  the  entire  frequency  range  of  the 
human  voice.  In  other  words,  it  must  deal  with  very  complex  alter- 
nating currents. 

1  The  early  inventors  who  attacked  the  problem  naturally  thought  of  the  simple 
device  of  applying  a  microphonic  contact  immediately  to  the  vibrating  diaphragm 
of  a  telephone,  hoping  to  repeat  the  almost  infinitesimal  vibrations  of  this  dia- 

1  Abstract  from  an  article  by  Professor  John  Trowbridge  in  the  Philosophical  Magazine. 

399 


400  TOLL  TELEPHONE  PRACTICE 

phragm,  and  to  give  them  an  increase  of  energy  by  a  local  battery.  This  attempt 
is  an  application,  pure  and  simple,  of  the  principle  of  the  telegraph  relay  and, 
therefore,  marks  no  progress  in  the  art;  for  it  was  not  new  in  principle  and  further- 
more did  not  work.  The  application  of  the  microphonic  contact  loaded  the  dia- 
phragm at  its  most  sensitive  point  and  thus  prevented  the  vibrations  which  one 
sought  to  repeat;  moreover,  the  vibrations  of  the  diaphragm  are  too  minute  to 
cause  a  sufficient  agitation  of  the  microphonic  contact. 

The  next  step,  in  the  mind  of  the  inventor,  was  to  endeavor  to  increase  the 
vibrations  of  the  center  of  the  diaphragm  by  a  lever.  This  arrangement  was 
found  to  be  inoperative,  for  the  short  arm  of  the  lever  exercised  a  prejudicial 
pressure  on  the  vibrating  diaphragm;  moreover,  the  fundamental  vibrations  of 
the  lever  were  superposed  on  the  vibrations  of  the  diaphragm,  thus  completely 
confusing  the  speech. 

It  must  be  remembered  that  the  telephone  is,  after  all,  an  imperfect  instrument 
and  its  wonderful  adaptiveness  is  greatly  aided  by  the  human  brain,  which  catches 
at  the  connection  of  thought.  This  can  be  seen  if  individual  words  are  transmitted 
without  context.  Moreover,  the  amount  of  energy  utilized  in  the  telephone  is 
extremely  small;  most  of  the  energy  of  the  currents  which  actuate  it  and  transmit 
speech  is  dissipated  in  heat.  Some  observers  think  that  less  than  one  per  cent  of 
the  energy  of  such  current  is  transformed  into  sound  waves.  We  see,  therefore, 
that  the  problem  of  the  telephone  relay  calls  for  all  our  electrical  and  mechanical 
aids  to  preserve  and  transmit  this  small  percentage. 

Since  mechanical  enlargement  of  the  vibration  of  the  telephonic  diaphragm  by 
levers  is  out  of  the  question,  the  next  more  promising  step  seems  to  be  the  bringing 
in,  so  to  speak,  of  electromagnetic  energy.  This  method  gets  rid  of  mechanical 
pressure  on  the  vibrating  diaphragm  of  the  telephone  and  substitutes  an  electric 
pressure  without  any  visible  connections  between  the  circuits.  This  method  also 
is  ineffective.  It  has,  however,  a  certain  analogy  to  another  and  more  successful 
attempt  to  utilize  an  invisible  and  intangible  magnetic  effect  without  bringing  a 
mechanical  pressure  on  the  telephonic  diaphragm;  this  method  consists  in  causing 
the  telephone  currents  to  disturb  a  piece  of  iron,  a  balance  magnet,  or  a  suspended 
coil  in  a  strong  magnetic  field  such  as  is  found  at  the  center  of  an  electromagnet 
or  between  the  poles  of  a  strong  permanent  magnet. 

The  principle  of  this  method  is  that  of  the  siphon  recorder,  the  invention  of 
Lord  Kelvin,  which  is  used  on  ocean  cables.  Since  the  current  on  the  cable  is 
very  feeble,  and  cannot  work  ordinary  telegraph  instruments,  some  method  must 
•be  used  to  magnify  or  record  the  signals.  The  method  adopted  by  Lord  Kelvin 
was  that  of  a  delicately  suspended  coil  so  placed  between  the  poles  of  a  powerful 
magnet  that,  when  the  feeble  currents  passed  through  this  coil,  it  oscillated;  for 
the  feeble  currents  animated  the  coil  making  it  an  electromagnet,  the  poles  of 
which  sought  the  poles  of  the  powerful  stationary  magnet.  Thus  a  very  feeble 
current  could  be  detected  by  the  powerful  magnetic  influence  to  which  it  was 
subjected.  Here  we  have  a  mechanical  movement  of  a  vibrating  system,  produced 
without  the  intermediation  of  visible  connecting  parts.  The  same  principle  has 
been  adopted  in  many  forms  of  instruments  for  detecting  and  measuring  electrical 
currents  both  in  laboratories  and  in  commercial  electrical  installations.  It  has, 


THE  TELEPHONE  REPEATER 


401 


therefore,  occurred  to  many  that  by  the  use  of  this  principle  of  magnifying  the 
vibrations  of  moving  parts  by  the  reaction  between  the  feeble  currents  in  s»ch 
parts  and  the  environment  about  these  parts,  one  should  be  able  to  strengthen 
vibrations.  The  mechanical  difficulties,  however,  are  very  great  if  one  endeavors 
to  apply  this  principle  to  the  problem  of  the  telephone  relay.  A  delicate  suspen- 
sion, such  as  that  used  in  the  siphon  recorder  or  the  D'Arsonval  galvanometer,  is 
out  of  the  question;  and  a  rigid  suspension  prevents  the  turning  movement,  or 
the  seeking  of  the  poles  of  the  powerful  magnet  by  the  coil  which  conveys  the 
feeble  currents.  A  certain  measure  of  success,  however,  can  be  obtained  by  care- 
ful adjustments  in  the  laboratory,  but  the  utilization  of  the  turning  movement  of 
a  coil  in  a  magnetic  field  has  not  yet  proved  of  commercial  use  in  telephony. 

We  are  apparently  brought  back  to  some  modification  of  the  simple  principle 
of  the  disturbance  of  a  powerful  magnetic  field  by  the  effect  of  feeble  currents 
circulating  around  coils  placed  in  such  fields.  Suppose,  for  instance,  that  we  have 
a  hollow  electromagnet  with  another  electromagnet  suspended  above  it,  the  iron 
core  of  the  suspended  magnet  forming  a  part  of  the  core  of  the  stationary  and 
more  powerful  magnet.  The  system,  evidently,  can  be  balanced  in  various  ways; 
for  instance,  the  suspended  magnetic  core  can  be  maintained  in  a  definite  position 
by  connection  with  a  telephone  diaphragm,  and  when  a  feeble  current  circulates 
through  the  coil  of  such  a  suspended  electromagnet,  its  position  with  respect  to 
the  stationary  coil  will  change.  Instead  of  the  diaphragm  of  a  telephone,  it  is 
evident  that  a  diaphragm  connected  to  a  microphonic  contact  may  be  employed. 
This  idea  can  be  found  in  the  efforts  of  many  inventors  to  construct  a  relay.  Pro- 
fessor Dolbear  has  described  a  telephone  which  works  upon  this  principle;  a  non- 
magnetic diaphragm  placed  close  to  the  pole  of  a  permanent  magnet  carries  a 
small  electromagnet  which  is  balanced  under  the  influence  of  the  elasticity  of  the 
diaphragm  and  the  magnetism  of  the  permanent  magnet.  When  the  voice  causes 
the  diaphragm  to  vibrate,  the  movements  of  the  electromagnet  disturb  the  mag- 
netic field,  producing  feeble  currents  of  induction  in  the  moving  coil,  which  trans- 
mits speech  to  a  similar  piece  of  apparatus.  If  this  similar  piece  of  apparatus 
had  been  employed  to  modify  a  microphonic  contact,  it  would  have  been  the 
precursor  of  many  subsequent  inventions. 

Instead,  therefore,  of  the  turning  or  torsional  effect  relied  upon  to  actuate  Lord 
Kelvin's  siphon  recorder  —  called  "  siphon  "  because  a  siphonic  pen  records  the 
oscillations  of  the  vibrating  coil  —  we  have  efforts  to  utilize  the  to-and-fro  thrust 
of  a  vibrating  core  of  an  electromagnet,  whose  position  in  a  powerful  field  is  modi- 
fied by  the  strength  of  the  feeble  currents  which  circulate  around  its  core. 

At  first  sight,  it  would  seem  that  the  inertia  of  the  suspended  electromagnet,  or 
that  of  its  core  or  plunger  if  the  coil  of  the  electromagnet  is  fixed,  would  be  so 
great  that  the  motion  of  the  microphonic  contacts  would  be  seriously  impeded. 
It  is  true  that  the  weight  of  the  vibrating  parts  in  this  form  of  relay  must  be  small 
and  there  must  not  be  any  subsidiary  vibrations  of  the  moving  parts  which  might 
be  superposed  upon  the  vibrations  due  to  the  telephonic  currents.  It  is  evident 
that  such  subsidiary  vibrations  can  arise  if  the  moving  parts  are  long  and  of  con- 
siderable size.  With  a  loaded  microphonic  contact  we  obtain  either  feeble  effects, 
or  roaring  sounds  resembling  in  effect  the  results  obtainable  if  the  membrane  of 
the  ear  is  loaded  by  an  obstruction. 


402  TOLL  TELEPHONE  PRACTICE 

In  this  form  of  telephone  relay,  therefore,  we  have  a  microphonic  contact  con- 
nected with  what  may  be  called  an  iron  plunger,  whose  position  in  a  magnetic 
field  is  modified  by  changes  in  its  magnetism  produced  by  feeble  telephonic  cur- 
rents. The  only  mechanical  connection  is  that  of  the  moving  plunger  with  the 
microphonic  contact. 

The  magnetic  portion  of  a  relay  embodying  these  ideas  can  be  suitably  con- 
structed so'  as  to  perform  its  part  with  a  commercial  degree  of  perfection.  The 
principal  imperfections  of  the  relay  arise  from  its  microphonic  element.  Among 
such  imperfections  the  most  notable  one  is  the  roaring  of  the  microphone  when  a 
strong  battery  is  used  to  get  the  greatest  degree  of  sensitiveness  from  it.  This 
noise,  which  arises  in  great  part  from  crepitations  produced  by  heat,  can  com- 
pletely overpower  telephonic  transmission  of  speech.  This  crepitation  is  greatly 
enhanced  by  the  direct  connection  of  the  plunger  or  moving  electromagnetic  coil 
with  the  microphonic  contact;  for  the  movements  in  the  magnetic  field  and  the 
crepitation  in  the  microphone  get  into  synchronism,  mutually  aiding  each  other. 
This  mutual  action  is  one  of  the  greatest  barriers  to  the  perfection  of  a  telephone 
relay  in  which  a  close  connection  exists  between  the  parts  moving  in  the  magnetic 
field  and  the  microphonic  contacts.  To  overcome  this  defect  would  be  a  great 
service  to  the  art  of  telephony.  _ 

The  design  of  the  commercial  repeater  used  by  the  American  Tele- 
phone and  Telegraph  Company,  the  invention  of  Mr.  H.  E.  Shreeve, 
is  a  development  of  the  type  in  which  a  powerful  stationary  field  and 
a  movable  coil  are  employed.  Particular  attention  has  been  given 
to  the  radiation  of  the  heat  generated,  so  that  continuous  operation 
is  possible.  The  best  understanding  of  this  apparatus  can  be  obtained 
from  the  specification  of  Mr.  Shreeve's  fundamental  patent,  which  is 
quoted  in  what  follows. 

"  In  carrying  out  my  invention  I  employ  and  adapt  for  connection  at  any  point 
between  transmitting  and  receiving  stations  of  a  telephone-circuit  or  series  or 
sequence  of  circuits  an  organization  comprising  a  variable  receiving-magnet 
responsive  to  the  talking-currents  of  such  transmitting-station  and  a  variable- 
resistance  medium  mounted  in  operative  relation  to  the  said  receiving-magnet  to 
be  acted  upon  thereby  and  arranged  to  forward  the  talking-currents  with  renewed 
energy  and  without  impairment  of  their  quality  characteristics  to  such  receiving- 
station  for  the  more  perfect  operation  of  the  receiving  instrument  there. 

In  the  development  of  this  invention  it  has  been  found  important  (keeping  in 
mind  the  character,  delicacy,  and  minuteness  of  the  forces  engaged,  the  smallness 
of  the  motion,  and  the  functions  to  be  exercised)  that  the  inertia  of  the  moving 
parts  shall  be  as  small  as  possible,  that  the  magnetizing  and  magnetization- varying 
forces  shall  be  so  organized  and  disposed  that  the  maximum  effect  of  the  latter 
upon  the  former  shall  occur  at  the*  strongest  part  of  the  common  field,  that  the 
maximum  effect  of  both  may  be  concentrated  directly  upon  the  active  or  movable 
member  of  the  transmitting  medium,  and  preferably  upon  the  most  sensitively 


THE  TELEPHONE  REPEATER 


403 


mobile  part  or  point  thereof,  and  that  provision  shall  be  made  to  facilitate  the 
expeditious  dissipation  of  the  heat  developed  in  and  by  the  operation  of  the  traqs- 
mitting  medium.  These  principles  are  exemplified  by  the  present  invention  and 
in  its  receiving  and  transmitting  elements,  which  are  closely  associated  in  a  single 
instrument. 

The  receiving  factor  comprises  a  magnet  constituting  the  required  initial  mag- 
netic field,  a  magnetization-varying  coil  to  be  connected  with  the  main  circuit  of 
the  original  transmitter  to  receive  the  talking-current  thereof  and  encompassing 
the  end  of  the  magnet,  which  thus  serves  as  a  fixed  core  or  pole-piece  entering  said 
coil  to  have  its  magnetization  varied  thereby,  and  a  short  and  light  piece  of  iron 
which  forms  a  movable  pole-piece  whose  end  is  closely  adjacent  to  that  of  the  fixed 
pole-piece  in  the  magnetic  field.  The  transmitting  factor  closely  confronting  the 
said  coil  is  a  variable-resistance  microphone  and  has  a  movable  contact  or  electrode, 
which  instead  of  being  actuated  by  a  vibratory  diaphragm  in  the  usual  manner  is 
attached  directly  to  the  light  movable  pole-piece  of  the  receiving  part  of  the  appa- 
ratus, which  thus  constitutes  a  direct  magnetic  connection  between  the  receiving- 
magnet  and  the  transmitting  medium,  and  by  this  arrangement  the  diaphragm  is 
dispensed  with,  the  inertia-  of  the  moving  parts  reduced  to  a  minimum,  and  the 
requisite  motion  imparted  to  the  movable  electrode  of  the  transmitting  medium 
directly  from  the  variable  field  and  preferably  from  the  center  of  the  varying-coil, 
and  therefore  from  the  most  effective  part  of  said  field. 

The  magnet  establishing  the  initial  field  may  be  either  an  electromagnet  of  any 
construction  or  form  excited  by  a  separate  magnetizing-coil  in  a  special  local  circuit 
or  a  permanent  magnet  such  as  that  of  the  ordinary  and  standard  telephone- 
receiver.  An  electromagnet  is,  however,  to  be  preferred  for  this  purpose,  since  in 
association  with  it  an  adjustable  resistance  may  be  included  in  its  local  circuit  to 
regulate  the  strength  of  its  current,  and  thereby  the  strength  of  the  magnet,  and 
thus  of  the  initial  field,  to  any  desired  degree.  Furthermore,  I  find  it  of  distinct 
advantage  to  provide  that  the  electromagnet  shall  be  of  tubular  form,  having  an 
iron  shell,  with  the  magnetizing  and  varying  coils  arranged  concentrically  therein, 
to  surround  the  fixed  core  or  pole-piece,  the  said  magnetizing-coil  being  preferably 
outermost  and  the  iron  shell  or  casing  arranged  to  entirely  inclose  both  coils  except 
at  their  front  center,  where  an  opening  or  perforation  is  provided  to  receive  the 
movable  pole-piece  attached  to  the  transmitter-electrode,  which,  passing  through 
said  opening  into  the  varying-coil,  constitutes  a  portion  of  the  magnetic  circuit  of 
the  receiving-magnet.  For  the  avoidance  of  eddy-currents  the  iron  shell  may  be 
slit  longitudinally  down  one  side  and  to  the  center  of  its  front  plate. 

The  variable-resistance-transmitting  medium  is  of  the  "  Runnings  "  and  "  solid- 
back  "  types,  wherein  a  mass  of  granular  carbon  is  held  inclosed  in  a  flat  chamber 
or  hollow  button  between  rigid  and  vibratory  conducting-disks  (usually  of  carbon), 
which  respectively  constitute  contact  members  or  electrodes,  one  of  which  is 
vibratory  or  movable,  the  mechanical  connection  of  the  latter  with  the  light 
movable  pole-piece  of  the  receiving-magnet  being  made  at  its  center,  that  being 
the  point  or  part  most  sensitive  and  most  readily  mobile  and  having  the  widest 
range  of  motion. 

By  inclosing  the  working  parts  of  the  apparatus  and  particularly  the  trans- 


404 


TOLL  TELEPHONE  PRACTICE 


nutting  element  thereof  in  a  metal  casing  possessing,  or  in  connection  with,  con- 
siderable mass  and  radiating-surface  and  with  which  such  working  parts  are  in 
heat-conducting  relation  an  effectual  means  is  provided  for  the  prompt  and  con- 
tinuous removal  and  dissipation  of  the  heat,  which  during  the  operation  of  the 


FIG.  270.  —  Construction  of  Shreeve  Repeater. 

instrument  is  generated  in  the  transmitter-button  by  the  passage  of  the  local- 
circuit  current  through  the  variable-resistance  material  and  which  if  retained  and 
permitted  to  accumulate  acts  to  deprive  the  carbon  granules  of  their  microphonic 
property,  and  thus  seriously  impairs  the  operation  of  the  transmitting  medium. 


THE  TELEPHONE  REPEATER 


405 


In  the  drawings  accompanying  this  specification,  Fig.  i  is  a  perspective  view 
showing  the  external  appearance  of  a  form  of  apparatus  embodying  the  invention 
which  has  been  made  and  successfully  used.  Fig.  2  is  a  vertical  longitudinal  sec- 
tion of  Fig.  i,  taken  on  the  line  xx  of  Fig.  3,  showing  the  preferred  construction 
and  arrangement  of  the  parts.  Fig.  3  is  an  end  view  of  the  apparatus  shown  by 
Figs,  i  and  2.  Fig.  4  illustrates  the  mounting  of  the  transmitting  medium  with 
the  movable  core  of  the  receiving-magnet  attached  to  its  movable  electrode,  Figs.  5, 
6,  and  7  showing,  respectively,  the  end  view  of  the  said  medium  and  its  mounting 
and  separate  side  and  front  views  of  the  said  electrode  and  the  core  attached 
thereto.  Figs.  8,  9,  and  10  show  in  detail  rear,  side,  and  front  views  of  the  tubular 
magnet  preferably  employed  in  the  receiving  medium.  Fig.  n  is  a  diagram  show- 
ing the  electrical  connections  of  the  renewer  or  reinforcing  apparatus  when  asso- 
ciated with  a  telephone-circuit  at  an  intermediate  point  thereof.  Fig.  1 2  illustrates 
a  modified  arrangement  for  establishing  the  initial  field  of  the  receiving  medium 
and  an  alternative  circuit  arrangement  for  the  apparatus  as  a  whole.  Fig.  13 
illustrates  still  another  mode  of  constituting  the  initial  magnetic  field  of  force,  and 
Fig.  14  is  a  diagram  of  the  manner  of  supplying  the  initial  field  for  the  form  of 
electromagnet  illustrated  by  Figs,  i  and  2. 

Referring  to  the  drawings,  and  for  the  present  more  particularly  to  Figs,  i  to 
10  and  14,  the  working  parts  are  inclosed  in  a  cylindrical  metal  casing  C,  screwed 
or  bolted  to  a  chambered  and  centrally-bored  metal  standard  A,  wrhich  in  turn  is 
mounted  upon  a  metallic  base  B,  to  which  it  is  secured  in  any  desired  way,  as  by 
screws  a,  which  pass  through  said  base  and  into  the  lower  edge  of  the  standard. 
The  outer  end  of  the  casing-cylinder  C  is  closed  by  a  disk  Z),  of  hard  rubber  or  like 
material,  secured  to  its  edge  by  screws  d.  M  is  the  variable  magnet  constituting 
the  receiving  factor  or  medium  of  the  instrument,  and  V  the  variable-resistance- 
transmitting  medium.  The  former  (illustrated  by  Figs.  2,  8,  9,  10,  and  14)  is  in 
this  instance  an  electromagnet  of  the  tubular  or  iron-clad  type,  having  a  fixed  iron 
core  or  pole-piece  p,  a  movable  iron  pole-piece  /,  an  inclosing  iron  shell  e,  a  mag- 
netizing or  exciting  coil  m,  and  a  magnetization-varying  coil  n.  It  is  attached  as 
a  whole  by  screws  b  to  the  insulating-disk  D,  which  has  binding-screws  5  to  serve 
as  terminals  for  the  said  coils  and  is  centrally  perforated  to  receive  a  threaded  iron 
socket  g,  through  which  passes  the  shank  r  of  the  fixed  core  p.  The  magnetizing- 
coil  m  and  varying-coil  n  are  concentrically  disposed  within  the  iron  shell  e,  the 
said  magnetizing-coil  being  preferably  outermost.  The  shell  itself  is  closed  in 
front  by  the  plate  e3,  which,  however,  may,  as  shown,  be  an  extension  of  the  sub- 
stance of  the  shell  spun  or  struck  up  from  the  cylindrical  part  thereof  and  has  for 
a  heel-plate  the  thick  disk-formed  base  g2  of  the  socket  g,  being  provided  rear- 
wardly  with  a  flange  e2,  overlapping  and  closely  clasping  the  edge  of  said  base- 
plate, so  that  both  coils  are  entirely  inclosed  by  the  said  shell  with  the  exceptions 
of  a  small  opening  or  aperture  e4  at  the  center  of  the  front  plate,  forming  a  passage 
for  the  movable  pole-piece  /,  and  a  longitudinal  slit  e5,  extending  from  the  said 
aperture  and  down  the  side  of  the  shell  to  prevent  the  development  and  circulation 
of  eddy-currents  and  consequent  waste  of  energy.  The  fixed  core  p  may,  as  shown, 
be  fitted  at  its  outer  end  with  a  bolt-head  rz  and  jam-nut  r3  or  other  means  for 
turning  it  and  holding  it  in  place,  and  its  shank  r  is  threaded  to  correspond  with 


406  TOLL  TELEPHONE  PRACTICE 

the  internal  thread  of  its  socket  g.  Entering  the  coils  through  said  socket,  it 
passes  to  or  nearly  to  the  center  thereof,  and  being  magnetized  by  the  coil  m,  which 
receives  energy  from  the  battery  S  in  the  local  circuit  7,  Fig.  14,  it  acts  to  establish 
the  initial  magnetic  field.  R  is  a  rheostat  or  adjustable  resistance  connected  in  the 
local  circuit  7  to  regulate  the  strength  of  the  magnetizing-current,  and  by  thus 
providing  the  receiving  medium  of  the  apparatus  with  an  electromagnet  separately 
excited  by  a  special  source  in  local  circuit  and  with  such  means  of  current  regula- 
tion the  magnet  may  readily  be  regulated  to  produce  the  desired  power.  The 
movable  iron  core  or  pole-piece  /  is  a  short  piece  of  small-sized  iron  rod  and  is 
attached  at  one  end  to  a  movable  part  of  the  associated  transmitting  medium  in  a 
manner  presently  to  be  explained,  and  being  thereby  elastically  supported  it  passes 
loosely  through  the  aperture  e4  and,  as  best  shown  in  Fig.  2,  into  the  forward  end 
of  the  inclosed  coils  m  and  n,  extending  to  a  point  about  the  center  thereof,  so  that 
its  inner  end  nearly  reaches  but  does  not  touch  that  of  the  fixed  core  p  in  the  con- 
centrated field  at  the  center  of  said  coils.  The  distance  between  the  ends  of  the 
fixed  and  movable  cores  may,  it  is  evident,  be  accurately  adjusted  by  turning  the 
former  in  its  threaded  socket  g.  The  magnetic  system  of  the  receiving  agency 
when  constructed  as  shown  and  described  constitutes,  it  will  be  seen,  an  approxi- 
mately complete  magnetic  circuit  having  fixed  and  movable  or  vibratory  pole- 
pieces  at  the  center  of  exciting  and  varying  coils,  and  thus  at  the  point  of  highest 
magnetizing  power  and  at  the  most  effective  part  of  the  magnetization-varying 
field  and  whose  only  substantial  gap  in  the  continuity  of  its  iron  is  that  which  is 
formed  by  the  space  between  said  poles.  The  magnetization-varying  coil  n  is 
designed  to  be  connected  with  the  main  circuit  or  circuit-section  E  and  to  be  ex- 
cited by  the  voice-currents  flowing  therein  and  proceeding  from  the  original  trans- 
mitting-station  of  such  circuit.  It  encompasses  both  pole-pieces  and  is  adapted 
to  vary  the  initial  magnetization  and  mutual  attraction  of  both,  and  consequently 
to  throw  the  movable  core  or  pole-piece  into  vibrations  corresponding  to  such 
attraction  variations  and  to  the  electrical  variations  or  voice-currents  of  the  circuit. 
The  ends  of  the  windings  of  the  coils  m  and  n  pass  through  insulated  apertures  3, 
4,  5,  and  6  in  the  socket-plate  g2  and  then  to  the  terminal  binding-screws  s  on  the 
exterior  of  the  non-conducting  disk  D,  whereby  they  may  be  attached  to  the  local 
and  main  circuit  conductors,  respectively.  The  transmitting  medium  7,  closely 
confronting  the  forward  end  of  the  magnet  M,  is  suitably  mounted  within  the 
casing  C,  the  metal  standard  A ,  which  closes  one  end  of  said  casing,  being  recessed 
at  c  for  its  reception.  It  mainly  consists  of  a  metal  chamber  or  hollow  button  h, 
in  type  and  form  substantially  identical  with  that  employed  in  standard  telephone- 
transmitters  having  a  non-conducting  internal  periphery  ft  and  forward  and  back 
contact  members  or  electrodes  v  and  z,  with  granular  carbon  o  inclosed  between 
them.  The  electrodes  are  insulated  from  each  other  at  their  edges  by  the  said 
peripheral  non-conductor,  and  the  metal-containing  case  has  an  elongated  stud 
or  sleeve  Z,  passing  through  the  central  bore  of  the  standard  A  to  form  its  support 
and  containing  a  rod  k,  insulated  by  a  non-conducting  bushing  H  and  terminating 
externally  in  a  binding-screw  connection  /.  The  back  electrode  z  is  a  carbon  plate 
fixed  to  the  end  within  the  chamber  h  of  the  insulated  rod  k  and  is  itself  insulated 
from  the  metal  case  or  its  attached  stud.  Its  connection  with  the  primary  circuit 


THE  TELEPHONE  REPEATER  407 

N  of  the  transmitting  medium  is  formed  through  the  said  insulated  rod  k  and  by 
means  of  the  conductor  w,  attached  thereto.  The  forward  and  movable  electrode 
v,  also  preferably  carbon,  is  a  thin  plate  held  in  place  to  close  the  chamber  h  on 
its  side  toward  the  magnet  by  the  ordinary  clamping-ring  y,  which  screws  over  the 
threaded  exterior  of  the  said  chamber  h.  This  electrode  having  considerable 
elasticity  is  readily  vibratory  and  is  in  electrical  connection  with  the  said  primary 
circuit  N  through  the  metal  chamber-casing,  the  stud  Z,  the  standard  A,  and  the 
base  B,  to  which  the  conductor  w1  of  said  circuit  is  attached  at  the  screw  /*.  As 
indicated  by  the  diagram,  Fig.  1 1,  the  local  circuit  N  includes  the  source  of  renewed 
energy  S*  and  the  primary  winding  of  the  induction  coil  or  coils  /.  The  movable 
electrode  v  is  rigidly  attached  at  its  center  to  the  outer  end  of  the  movable  pole- 
piece  /,  and  thus  forms  the  external  elastic  support  of  the  said  pole-piece  and 
receives  motion  therefrom  without  the  intervention  of  any  diaphragm.  In  an  ap- 
paratus of  this  class  sensitiveness  to  slight  moving  forces  and  celerity  of  action  is 
more  important  than  a  relatively  wide  range  of  motion,  such  as  would  be  produced 
by  a  vibratory  diaphragm  or  armature  interposed  between  the  receiving  and 
transmitting  media,  and  I  have  found  that  by  dispensing  with  the  diaphragm  and 
by  securing  the  light  movable  pole-piece  /  of  the  magnetic  system  directly  to 
the  center  of  the  light  and  thin  movable  electrode  v  of  the  transmitting  medium 
the  requisite  sensitiveness  and  celerity  of  action  is  attained,  while,  moreover,  the 
actuating  forces  being  imparted  to  the  pole-piece  /,  and  as  a  consequence  to  the 
movable  electrode,  directly  from  the  varying  field  are  enabled  to  exercise  maximum 
effect.  /  is  a  radiating  block  or  mounting  centrally  bored  to  slide  over  the  pro- 
jecting end  of  the  elongated  stud  Z  of  the  transmitter-case,  having  considerable 
mass  and  scored  or  ridged,  as  atj,  to  increase  its  surface.  It  is  held  in  place  upon 
said  stud  by  the  washer/  and  nut/,  and  being  in  metallic  contact  with  the  said 
stud  and  also  with  the  heavy  metal  standard  A,  base  B,  and  casing  C  it  cooperates 
with  these  parts  to  conduct  away  from  the  variable-resistance  button  the  heat 
generated  therein  during  operation  and  to  dissipate  the  same  by  radiation. 

In  telephone  current  renewing  and  retransmitting  apparatus  constructed  in 
•accordance  with  the  foregoing  description  and  with  which  good  practical  results 
have  been  attained  the  magnetizing  or  local-circuit  coil  was  formed  of  two  hundred 
turns  of  No.  36  wire,  while  the  main  line  or  varying  coil  wound  next  to  the  cores 
consisted  of  fourteen  hundred  turns  of  No.  40  wire. 

The  current-renewing  apparatus  may  be  associated  with  telephone  main  circuits 
in  various  ways.  One  circuit  arrangement  with  which  it  has  been  successfully 
connected  and  employed  is  that  represented  by  Fig.  n  and  so  far  as  concerns  its 
receiving  factor  alone  by  Fig.  14  also.  In  this  arrangement  the  apparatus  is  shown 
as  being  placed  at  the  middle  of  a  long  circuit  and  between  the  sections  EE?  thereof, 
so  that  it  is  adapted  to  be  operated  indifferently  and  reciprocally  from  either  end 
of  the  line  and  to  renew  the  transmission  according  to  its  direction  from  either 
section  of  the  line  to  the  other. 

KK2  represent  keys  or  switches  which  when  in  the  position  shown  maintain 
the  direct  connection  of  the  circuit  through  the  section  E3  thereof,  the  renewing  or 
reinforcing  apparatus  being  disconnected.  In  this  position  the  circuit-conductor 
L  is  traceable  between  the  section-conductors  20  and  22  by  way  of  the  resting- 


408 


TOLL  TELEPHONE  PRACTICE 


contacts  14  and  16  of  keys  K  and  K2  and  their  uniting-conductor  21,  while  cir- 
cuit conductor  Lz  in  like  manner  extends  between  its  sections  23  and  25  through 
intermediate  conductor  24  and  its  terminal  contacts  15  and  17. 


Fig.  H. 


Fig.  12. 


JKZ 


-v. 


flg.14. 


FIG.  271.  —  Circuits  of  Shreeve  Repeater. 

By  moving  the  keys  or  switches  KKZ  to  their  alternative  position  the  conductors 
20  23  of  circuit-section  E  are  transferred  from  contacts  14  15  to  contacts  10  n 
and  the  conductors  22  25  of  section  E2  from  contacts  16  17  to  contacts  12  13,  so 
that  the  intermediate  section  E*  is  substituted  for  E3.  The  magnetization-varying 
coil  n  of  the  renewing-apparatus  receiving-magnet  is  connected  in  a  bridge  u  be- 


THE  TELEPHONE  REPEATER 


409 


tween  points  26  27  of  the  main  conductors  18  and  19  of  the  said  intermediate 
section  E*  and  is  thus  made  common  to  both  of  the  main  sections  EE*  to  be  operated 
by  the  distant  transmitter  of  either  one  —  that  is,  of  the  terminal  station  of  either 
section  —  according  to  the  direction  of  transmission  at  any  particular  moment  of 
time.  The  initial  magnetic  field  of  the  receiving  medium  may  be  established  by 
either  one  of  the  several  plans  indicated  by  Figs.  12,  13,  or  14,  respectively,  but, 
as  hereinbefore  stated,  preferably  by  that  of  Fig.  14.  The  transmitting  medium 
(indicated  conventionally)  is  included  in  the  local  circuit  N  and  is  adapted  to  have 
the  resistance  between  its  electrodes  v  and  z  varied  by  the  strength  variations  of 
the  magnet  M,  produced  by  the  voice-currents  in  the  varying-coil  n.  The  primary 
circuit./V  also  contains  the  primary  windings  i  of  induction-coils  /,  whose  secondary 
windings  j2  are  connected  one  on  either  side  of  the  bridge  u  and  in  the  conductors 
1 8  19,  respectively,  so  that  one  winding  is  in  main  section  E  and  the  other  in  main 
section  E2  of  the  through-circuit. 

It  is  to  be  understood  that  the  drawings  represent  the  electrical  arrangement 
only  and  that  in  practice  a  single  primary  winding  and  two  secondaries  may  be 
wound  over  a  single  core  and  into  a  single  induction-coil.  A  coil  having  a  single 
primary  winding  of  five  hundred  turns  of  No.  20  wire  with  a  resistance  of  about 
one  ohm  and  two  secondaries  wound  in  parallel  of  twelve  hundred  and  fifty  turns 
and  thirty  ohms  resistance  each  of  No.  29  wire  has  been  found  to  answer  well,  as 
has  also  a  varying-coil  for  the  receiving-magnet  formed  of  fourteen  hundred  turns 
of  No.  40  wire  having  a  resistance  of  about  one  hundred  and  thirty  ohms. 

If  desired,  the  apparatus  may  be  employed,  as  in  Fig.  1 2,  in  enabling  one  line- 
circuit  E5  to  retransmit  over  a  second  and  entirely  separate  circuit  E6.  Thus 
engaged  the  varying-coil  n  of  the  receiving  factor  or  agency  M  is  connected  in  the 
said  transmitting-circuit  E5  and  its  transmitting  medium  V  in  the  primary  local 
circuit  N  of  the  battery  S2,  together  with  the  primary  winding  i  of  an  induction- 
coil  P,  whose  secondary  winding  i2  is  wholly  connected  in  the  second  circuit  E6. 

As  hereinbefore  indicated,  while  a  compound  magnet  constructed  as  thus  far 
described  has  certain  advantages  it  is  not  essential,  and  other  modes  of  construct- 
ing in  accordance  with  the  foregoing  principles  the  magnet  system,  which  con- 
stitutes the  receiving  and  retransmitting  part  of  the  apparatus,  and  of  producing 
the  initial  and  varying  fields  may  be  adopted  without  any  departure  from  the  spirit 
of  the  main  invention.  For  example,  while  the  arrangement  of  the  fixed  and 
movable  pole-pieces,  which  has  been  specifically  described,  has  in  practice  been 
found  convenient  and  effective  and  has  particularly  commended  itself  as  being 
productive  of  highly-satisfactory  results  and  average  ordinary  conditions  it  is 
evident  that  the  relative  length  of  the  fixed  and  movable  pole-pieces  and  their 
relation  to  one  another  and  the  varying-coil  may  be  varied  within  limits  of  con- 
siderable width  to  suit  varying  conditions  of  service,  provided  always  that  the 
latter  pole-piece  shall  in  every  case  be  in  direct  connection  with  the  transmitting 
medium  and  that  the  two  poles  shall  closely  confront  each  other  without  contact, 
so  that  the  attraction  exercised  by  each  upon  the  other  may  readily  be  varied  by 
the  operation  of  the  varying-coil.  Such  modifications  in  construction  and  arrange- 
ment are  illustrated  in  Figs.  12,  13,  and  u.  Fig.  12  illustrates  a  modification 
wherein  the  magnetizing-coil  m  is  wound  over  the  hinder  part  of  the  fixed  core  p, 


410  TOLL  TELEPHONE  PRACTICE 

while  the  magnetization-varying  coil  n  alone  is,  as  in  the  forms,  placed  over  the 
adjacent  confronting  poles  of  said  core  and  the  adjacent  movable  core  /,  the  said 
poles  thus,  in  this  instance  also,  being  close  to  one  another  in  the  center  of  the 
varying  field.  Fig.  13  illustrates  another  modification  of  this  feature.  Here  the 
initial  field  of  the  magnetic  system  M  is  provided  by  a  permanent  magnet  m*,  the 
fixed  pole-piece  p  being  secured  thereto  and  being  magnetized  thereby  in  a  well- 
understood  manner.  This  arrangement  requires  one  coil  only  —  viz.,  the  line  or 
magnetization-varying  coil  n,  which  encompasses  the  confronting  poles  of  the  fixed 
and  movable  cores  p  and/,  which  approach  one  another  at  its  center,  or  thereabout. 
In  Fig.  ii  the  magnetic  receiving  medium  is  represented  as  having  the  fixed  pole- 
piece  p  extended  clear  through  the  bridged  varying-coil  n  and  to  a  point  flush  with 
or  a  little  beyond  the  forward  end  thereof,  while  the  movable  soft-iron  pole-piece 
/  is  made  very  short,  but  is  yet  directly  attached  to  and  supported  solely  by  the 
movable  contact  member  of  the  transmitting  member.  It  may  here  be  mentioned 
that  the  said  movable  contact  member  or  vibratory  electrode  should  be  very  thin 
and  elastic  and  that  I  have  found  a  carbon  disk  about  .01  of  an  inch  thick  to  answer 
admirably  and  to  be  both  strong  and  flexible.  In  all  cases,  however,  the  magnetic 
system  M  of  the  renewing  apparatus  may  properly  be  regarded  both  as  a  receiving 
and  a  retransmitting  medium,  for  by  its  varying-coil  it  receives  and  makes  use  of 
the  voice-currents  of  the  distant  transmitter,  and  by  its  movable  or  vibratory 
pole-piece  set  in  motion  by  said  coil  under  the  influence  of  such  voice-currents  it 
actuates  the  transmitting  medium  to  bring  a  new  source  of  energy  into  service." 

This  repeater  has  been  used  with  fair  success  on  the  New  York- 
Chicago  circuits,  situated  at  Pittsburg,  approximately  halfway  between 
terminals.  It  is  far  from  perfect,  however,  because  the  transmitting 
element  is  crowded  to  the  limit  of  its  capacity  and  severe  heating  is 
an  unavoidable  result.  The  efficiency  also  tends  to  fall  rapidly  after 
the  repeater  has  been  in  service  a  short  time.  For  this  reason,  these 
repeaters  are  usually  mounted  in  pairs  and  connected  to  a  double- 
throw  switch,  for  alternate  service. 


INDEX 


[The  figures  refer  to  page  numbers.] 


Arresters,    high    potential    and    abnormal 

current,    151. 

Adaptability  of  equipment  to  service,  59. 
Advantages  of  busy-test  key,  74. 

separate  toll  board,  59. 
American  Telegraph  and  Telephone  Co., 

equipment,  117. 
Ammeter  and   voltmeter  circuits,  wiring, 

220. 

Anchors,  various  types  of  guy,  289. 
Apparatus,  for  multiple-drop  board  circuits 
described,  107. 
distribution,  107. 

phantom  circuit,  installation,  237. 
small  test  panel,  arrangement,  243. 
used  in  various  circuits,  illustrated,  224. 
for  wire  stringing,  302. 
Apprcximate  sizes  of  poles,  262. 
Arrangement,  of  apparatus  for  small  test 

panel,  243. 

of  trunking  equipment,  69. 
Automatic  Electric  Company,  circuits,  for 
small    toll    installations    described, 
164. 

switchboard,  complications  arising  from 
toll  and  local  lines  terminating  in, 
156. 

systems,  toll  connections  to,  156. 
Auxiliary  toll  board  circuits,  103,  145. 

method  of  operating,  145. 
Average  life  of  poles,  261. 

Board,  non-multiple  common  battery,  47, 

66. 

Braces,  cross-arm,  278. 
Bridge  arnj  ratios,  table,  380. 
Bridge  circuit,  221. 

connections  for  measuring  resistance,  381. 
Bridging  telephones  for  rural  service,  15. 
Brush  and  tank  pole  treatments,  265. 
Busy-test  key,  advantages,  74. 


Busy-test  key,  on  two-way  toll  trunk,  74. 
methods  of  obtaining,  77. 

Cables,  recent  development  in  loading  un- 
derground, 332. 
results    obtained    in    tests    of    heavily 

loaded,  327. 

Cabling  and  size  of  wire  for  small  equip- 
ments, directions  regarding,  241. 
Calculagraph,   the,   a   valuable   time  and 

labor  saving  device,  63. 
Changes  in  switchboard  practice,  9. 
Character  of  magnetic   field   surrounding 

single  conductor,  336. 
Chief  operator,  duties,  165. 
equipment  for,  168. 
instruction  circuit  for,  170. 
telltale  circuit  for,  172. 
Circuit,  for  preliminary  tests,  181. 

repeating  coil  grounded-phantom,  212. 
Circuits,  of  the  Automatic  Electric  Com- 
pany for  small  toll  installations  de- 
scribed, 164. 

auxiliary  toll  board,  103,  145. 
Classes,  of  multiple  toll  boards,  75. 
of  test  and  morse  boards,  216. 
of  trouble,  analysis,  372. 
Classification  of  toll  board  equipments,  56. 
Cleat  wiring  in  phantom  transposition,  360. 
Climatic    conditions,    location    of    testing 

stations  under  various,  396. 
Combination    cord    circuit    for    multiple- 
drop  toll  board,  82. 
Combined    recording    and    common-drop 

section,  equipment,  no. 
Common    battery,    multiple    switchboard, 

50,  66. 

non-multiple  switchboard,  47,  66. 
Complications  arising  from  toll  and  local 
lines     terminating     in     automatic 
switchboard,  156. 


411 


412 


INDEX 


Composite,  ringer,  200. 
system    for   simultaneous   transmission, 

187. 

improvements  in,  8. 
metallic,  198. 

Compositing  telephone  lines,  195. 
Connecting  metallic  and  grounded  lines  by 

repeating-coil.  37. 
Construction,  of    phantom   transposition, 

362. 

of  repeating-coils,  36. 
of  Shreeve  repeater,  404. 
Copper  wire,  properties  of  hard-drawn,  251. 
temperature    effects    on    hard -drawn, 

256. 
Cord,  test  and  morse  board  preferable  for 

small  equipment,  226. 
circuit,  double  supervision,  27. 

repeating  coil  for  double  supervision, 

28. 

for  rural  service,  25. 

Cordless,  test  and  morse   boards   advan- 
tageous for  large  equipments,  226. 
test  and  morse  board,  face  equipment, 

233- 

Cross-arm  braces,  278. 
Cross-arms,  dimensions,  277. 
method  of  bracing,  278. 
Cross  talk    and    inductive    disturbances, 

334- 

Cut-off  jacks,  functions,  232. 
purposes  of,  explained,  229. 

Decay,  method  of  treating  poles  to  prevent, 

263. 

Description,  of    apparatus    for    multiple- 
drop  board  circuits,  107. 
method  of  operating  trunk  circuit,  80. 
of  operation  of  common  battery  multiple 

board,  50. 

of  toll  board  with  local  magneto  non- 
multiple  board,  65. 
of  Shreeve  repeater,  402. 
Designing  and  installing  lines,  engineering 

skill  requisite  for,  394. 
Detection  of  foreign  currents,  393. 
Different,  sizes  of  wire,  tensile  strength, 

252,  253. 
types  of  equipments  for  toll  switchboards, 

56. 
Dimensions  of  cross-arms,  277. 


Directions  regarding  cabling  and1  size  of 

wire  for  small  equipments,  241. 
Distribution  of    apparatus,  for    multiple- 
drop  board  circuits,  107. 
in  toll  line  terminal  explained,  148. 
and  installation  of  circuits  in  test  boards, 

222. 

and  setting  of  poles,  266. 
Disturbances,   transposing  lines  to  elimi- 
nate, 344. 
Double  supervision  cord  circuit,  27. 

repeating  cord  for,  28. 
Duplex  telephony,  Rosebrugh's  system,  5. 
Duties  of  chief  operator,  165. 
of  a  lineman,  398. 

Effect,  of  ice  formation  on  line  wire,  258. 
of   single   transmission   on   electrostatic 

induction,  342. 
single  transposition  on  electromagnetic 

induction,  342. 

of  sleet  and  wind  on  pole  lines,  271. 
Efficiency  of  rural  telephone  plant,  12. 
Eight-party  selective  system  for  metallic 

lines,  26. 
Electrical    and    mechanical    requirements 

for  line  wire,  250. 

Electromagnetic   and   electrostatic   induc- 
tion, 335. 
induction,  effect  of  single  transposition 

on,  342. 
Electrostatic    induction    between    parallel 

lines,  338. 

effect  of  single  transmission  on,  342. 
experimental   circuit   for  demonstrat- 
ing, 339- 
Engineering   skill   requisite   for   designing 

and  installing  lines,  394. 
Equipment    of   American    Telegraph    and 

Telephone  Co.,  117. 
arrangement  of  trunking,  69. 
chief  operator,  168. 

of    combined    recording    and    common- 
drop  section,  no. 
to  service,  adaptability,  59. 
of  testing  stations,  397. 
of   Tri-state   Telegraph  and  Telephone 

Co.,  130. 

for  two-position  toll  boards,  64. 
of  United  States  Telephone  Co.,  138. 
classification  of  toll  board,  56. 


INDEX 


413 


Equipment  for  toll  switchboards,  different 

types,  56. 

Essential  points  of  rural  telephone  plant,  15. 
Experimental    circuit    for    demonstrating 

electrostatic  induction,  339. 

Face  equipment  of  cordless  test  and  morse 

board,  233. 
Faults  caused  by  broken  ends,  tests  for 

locating,  390. 

Foreign  currents,  detection,  393. 
Forms  of  lightning  protectors,  37. 
Four-party  selective  system  for  grounded 

lines,  23. 
Functions  of  cut-off  jacks,  232. 

General  type  of  toll-to-toll  connection  for 

multiple-lamp  toll  boards,  112. 
Grounded  line,  selective  ringing  system  on, 

23- 

telephone  station  switch  for  two,  35. 
toll  cut-in  station  for,  34. 
two-party  selective  system  for,  23. 
and  metallic  lines,  switch  for  connecting, 

35- 

phantom  circuit,  repeating  coil,  212. 
Grounding-button  telephones,  17. 
Guy  anchors,  various  types,  289. 
Guy  wires,  methods  of  anchoring,  287. 
Guying  purposes,   miscellaneous   material 

for,  298. 

Hard-drawn  copper  wire,  properties,  251. 

temperature  effects  on,  256. 
High    potential    and     abnormal     current 
arresters,  151. 

Ice-coated  wire,  wind  pressure  on,  257. 
Ice  formation,  effect  of,  on  line  wire,  258. 
Improvements  in  composite  systems,  8. 
Improving  transmission,  Pupin's  method, 

by  inductive  loading,  7. 
Incoming  toll  trunk  for  non-multiple  toll 

board,  72. 

Induction,  effect  of  single  transmission  on 
electrostatic,  342. 
on  electromagnetic,  342. 
method  of  preventing,  340. 
Inductive  disturbances  and  cross  talk,  334. 
loading,   Pupin's  method  of  improving 
transmission  by,  7. 


Installation  of  apparatus  for  phantom  cir- 
cuit, 237. 
and  distribution  of  circuits  in  test  boards, 

222. 

Instruction  circuit,  chief  operator's,  170. 
Insulation  resistances,  measurement,  392. 
Interposition  trunk  circuit,  103. 

method  of  operating,  104. 
Iron  and  copper  wire,  table  of  resistance, 

376. 
Isolated  local  service,  2. 

Jack  and  key  equipment  for  single-position 

toll  boards,  62. 

Jack  panels  for  small  equipments,  240. 
Jacks,  functions  of  cut-off,  232. 
Jacob's  phantom  circuit  principle,  6. 
Joint  toll  and  local  offices,  78. 

local-to-toll  connections  in  three- 
wire,  92. 

toll-to-local  connections  in  three- 
wire,  96. 
three- wire  offices,  92. 

Key    equipment    at    toll    cut-in    station, 

method  of  wiring,  34. 
Key-type  equipment  at  toll  cut-in  station, 

39- 

Lay-out  of  a  toll  system,  58. 
Legless  telegraph  keys,  224. 
Leg-type  telegraph  key,  224. 
Lightning  protectors,  forms,  37. 
Line  construction,  245. 

wire,  effect  of  ice  formation  on,  258. 
mechanical     and     electrical     require- 
ments for,  250. 
specifications  for,  249. 
for  toll  lines,  247. 

Lines,  engineering  skill  requisite  for  de- 
signing and  installing,  394. 
systematizing  maintenance,  394. 
Loaded  cable,  results  obtained  in  tests  of 

heavily,  327. 
Local  service,  isolated,  2. 
and   toll   boards,  methods   of  handling 

connections  between,  66. 
switchboard,  toll  positions  at,  42. 
Local-to-toll  connections,  method  of  hand- 
ling, 83. 


414 


INDEX 


Local-to-toll  connections,  in  separate  toll 
and  local  three- wire  offices,  98. 
in  separate  two-wire  toll  and  local 

offices,  90. 
in   three-wire   joint   toll   and   local 

offices,  92. 

in  two-wire  joint  and  local  offices,  83. 
Locating    crosses,    procedure    in    making 

tests  for,  386. 
trouble,  371. 
Location  of  testing  stations  under  various 

climatic  conditions,  396. 
of  transposition  poles,  350. 

Magnetic    field    surrounding    single    con- 
ductor, character,  336. 
multiple    switchboard,    toll-to-toll    con- 
nection in,  47. 
Magneto  multiple  board,  46,  65. 

non-multiple  board,  43,  65, 
Maintenance  of  lines,  systematizing,  394. 
Measurement  of  insulation  resistances,  392. 
Mechanical  and  electrical  requirements  for 

line  wire,  250. 

Metallic  composite  systems,  198. 
lines,  eight-party  selective  systems  for, 

26. 

Method  of  bracing  cross-arms,  278. 
of  cabling  in  toll  line  terminal,  148. 
of  cutting  in  transpositions,  352. 
of  handling  local-to-toll  connections,  83. 
of  installing  test  conductors,  353. 
of  operating  auxiliary  toll  board  circuits, 

145- 

interposition  trunk  circuits,  104. 
trunk  circuit  described,  80. 
wire  chief's  testing  trunk,  182. 
of  preventing  induction,  340. 
of  transferring  toll  drops  for  night  service, 

61. 
6f  wiring  key  equipment  at  toll  cut-in 

station,  34. 
morse  circuits,  218. 
for  straight  telephone  circuit,  228. 
Methods  of  anchoring,  guy  wire,  287. 
of   connecting   wire   chief's   testing   ap- 
paratus to  toll  lines  described,  175. 
of  guying,  284. 
of  handling  connections  between   local 

and  toll  boards,  66. 
for  improving  rural  telephone  lines,  32. 


Methods  of  making  transpositions,  351. 
of  obtaining  busy  test,  77. 
of  testing  for  various  troubles,  370. 
of  transferring  toll  lines  for  night  service, 

60. 

of  treating  poles  to  prevent  decay,  263. 
Miscellaneous    material    for   guying    pur- 
poses, 298. 

Monitoring  and  morse  testing  circuits,  219. 
Morse  circuits,  method  of  wiring,  218. 
Multiple  board,  magneto,  46,  65. 
Multiple-drop  board  circuits  described,  ap- 
paratus for,  107. 

distribution  of  apparatus  for,  107. 
toll  board,  combination  cord   circuit 
for,  82. 
discussed,  92. 
switchboards,  75. 

Stromberg-Carlson,  97. 
lamp  board,  recording  circuit  for,  121. 

toll  switchboard,  112. 
switchboard,  common  battery,  50,  66. 

toll-to-local  connection  in  magneto,  47. 
toll  boards,  classes,  75. 
Multiplexing  single  wires,  schemes  for,  4. 
Murray  loop  test,  384. 

New  York-Chicago  telephone  line,  opening, 

6. 

Night  service,  method  of  transferring  toll- 
drops  for,  61. 

Nomenclature  of  equipment,  14. 
Non-multiple   switchboard,   common   bat- 
tery, 47,  66. 
magneto,  43,  65. 

toll  board,  incoming  toll  trunk  for,  72. 
recording  toll  trunk  for,  73. 

Objectionable  features  of  straight  bridging 

instruments,  16. 
Opening  of  New  York-Chicago  telephone 

line,  6. 
Operation    of    common    battery    multiple 

board  described,  50. 
of  telegraph  repeater  described,  192. 
of  toll  board  with  local  magneto  non- 
multiple  board  described,  65. 
of  two-wire  system  equipment,  130. 
of  wire  chief's  testing  circuit  described, 
178. 


INDEX 


415 


Operations  required  to  establish  complete 

connection  explained,  69. 
Order  wire,  phantom  circuit  as,  214. 

Parallel  lines,  electrostatic  induction  be- 
tween, 338. 

Paralleled  power  and  telephone  lines, 
transposition  problem  complicated 

by,  365- 
Phantom  circuit,  installation  of  apparatus 

for,  237. 

as  order  wire,  214. 
precautions  for  operating,  215. 
principle,  Jacob's,  6. 
retardation  coil,  211. 
lines,  211. 

transposition   applied   to   different   sys- 
tems, 357. 
cleat  wiring  in,  360. 
construction,  362. 
use,  repeating  coil  for,  213. 
Pole  line  routes,  246. 

lines,  effect  of  sleet  and  wind  on,  271. 
woods,  tensile  strength,  269. 
Poles,  approximate  sizes,  262. 
location  of  transposition,  350. 
selection  of  timber  for,  260. 
Precautions    for    operating   phantom    cir- 
cuit, 215. 

Preliminary  tests,  circuit  for,  181. 
Principle,  Jacob's  phantom  circuit,  6. 
Private  right-of-way  for  pole  lines  unde- 
sirable, 246. 
Procedure   in   making   tests   for   locating 

crosses,  386. 

Properties  of  hard-drawn  copper  wire,  251. 
Pulsating  and  alternating  current  telephone, 

switchboard  circuit  for,  21. 
telephone  on  grounded  line,  20. 
Pupin's  method  of  improving  transmission 

by  inductance  loading,  7. 
Purposes  of  cut-off  jacks  explained,  229. 

Railway  composite  systems,  206. 

Ratios,  table  of  bridge  arm,  380. 

Recent  developments  in  loading  under- 
ground cables,  332. 

Recording  circuit  for  multiple-lamp  board, 

121. 

positions,  shifting  receiving  circuit  at, 
105. 


Recording  toll  trunk  for  non-multiple  toll 

board,  73- 
Repeating   coil,   connecting   metallic*  and 

grounded  lines  by,  37. 
for  double  supervision  cord  circuit,  28. 
of  grounded-phantom  circuit,  212. 
method,  simplex  system  and,  188. 
for  phantom  use,  213. 
toll-to-toll  connection  with,  43. 
coils,  construction,  36. 
Resistance,  bridge  connections  for  measur- 
ing, 381. 

of  iron  and  copper  wire,  table,  376. 
line,  tests  to  ascertain,  380. 
Resistances,    measurement    of    insulation, 

392. 
Results  obtained  in  tests  of  heavily  loaded 

cables,  327. 
Retardation  coil  method,  189. 

of  phantom  circuit,  211. 
Right-of-way,  private,  for  pole  lines  un- 
desirable, 246. 
title  to,  246. 
Ringer,  composite,  200. 
Rcsebrugh's  system  of  duplex  telephony,  5. 
Running  wires  through  foliage,  30. 
Rural  service,  bridging  telephones  for,  15. 

cord  circuits  for,  25. 
telephone  equipment,  u. 
lines,  methods  for  improving,  32. 
plant,  efficiency,  12. 

essential  points,  15. 
toll  service,  32. 

Sag  of  telephone  and  telegraph  wires,  259. 
Schemes  for  multiplexing  single  wires,  4. 
Season  of  the  year  to  cut  poles,  261. 
Section,  equipment  of  combined  recording 

and  common-drop,  no. 
Selection  of  timber  fpr  poles,  260. 
Selective  ringing  system  on  grounded  line, 

23- 
system  for  grounded  lines,  four-party,  23. 

metallic  lines,  eight-party,  26. 
Separate  toll  board,  advantages,  59. 

and  local  offices,  toll-to-local  connec- 
tions in  two-wire,  86. 

two- wire,  86. 
three-wire  offices,  98. 
three-wire  offices,  local-to-toll  con- 
nections in,  98. 


416 


INDEX 


Separate  toll  board,  toll-to-local  connec- 
tions in,  102. 

two-wire  toll  and  local  offices,  local-to- 
toll  connections  in,  90. 
Setting  and  distribution  of  poles,  266. 

poles,  280. 

Shifting  receiving  circuit  at  recording  posi- 
tion, 105. 
Shreeve  repeater,  construction,  404. 

description,  402. 
two-way  repeater,  399. 
Simplex  line,  terminal  telegraph  station  on, 

192. 
system  and  repeating  coil  method,  188. 

for  simultaneous  transmission,  187. 
systems,  theory,  187. 

Simultaneous  transmission,  composite  sys- 
tem for,  187. 
simplex  system  for,  187. 
Van  Rysselbergh's  system,  4. 
Single-position  toll  boards,  jack  and  key 

equipment  for,  62. 
wires,  schemes  for  multiplexing,  4. 
Sleet  and  wind  on  pole  lines,  effect,  271. 
Small  equipments,  jack  panels  for,  240. 
magneto   switchboard,    toll-to-toll   con- 
nection at,  42. 

switchboard,  wiring  toll  terminal  for,  41. 
test  panels,  237. 
toll  switchboards,  59. 
Special  equipment  for  supervision,  165. 
Specifications  for  line  wire,  249. 
Stations,  equipment  of  testing,  397. 

toll  cut-in,  29. 

Steel  and  concrete  poles,  262. 
Straight  bridging  instruments,  objection- 
able features,  16. 
telephone  circuit,  method  of  wiring  for, 

228. 

Stresses  to  which  poles  are  subjected,  267. 
Stromberg-Carlson       multiple-drop       toll 

switchboard,  97. 
Subscribers'  instrumefts,  14. 
Supervision,  special  equipment  for,  165. 
Switch  for  connecting  grounded  and  me- 
tallic lines,  35. 
telephone  station,  for  two  grounded  lines, 

35- 

Switchboard  circuit  for  pulsating  and  al- 
ternating current  telephone,  21. 
common  battery  multiple,  50,  66. 


Switchboard,  non-multiple,  47,  66. 

magneto  non-multiple,  43,  65, 

practice,  changes  in,  9. 

toll  positions  at  local,  42. 
Switchboards,    different    types    of    equip- 
ments for  toll,  56. 

small  toll,  59. 

Systematizing  maintenance  of  lines,  394. 
Systems,  composite,  195. 

improvements  in  composite,  8. 

Table  of  bridge  arm  ratios,  380. 

resistance  of  iron  and  copper  wire,  376. 
Tank  pole  treatments,  brush  and,  265. 
Telegraph  key,  leg-type,  224. 
keys,  legless,  224. 

repeater,  operation,  described,  192. 
Telephone  circuit,  method  of  wiring  for 

straight,  228. 

line,  opening  of  New  York-Chicago,  6. 
plant,  efficiency  of  rural,  12. 

essential  points  of  rural,  15. 
station  switch  for  two  grounded-lines,  35. 
and  telegraph  wires,  sag,  259. 
Telephones,  bridging,  for  rural  service,  15. 

grounding-button,  17. 
Telltale  circuit  for  chief  operat6r,  172. 
Temperature  effects  on  hard-drawn  copper 

wire,  256. 
Tensile  strength  of  different  sizes  of  wire, 

252,  253. 
pole  woods,  269. 
Terminal  telegraph  station  on  simplex  line, 

192. 

wiring  of  toll  line,  148. 
Test  boards,  installation  and  distribution 

of  circuits  in,  222. 

conductors,  method  of  installing,  353. 
and  morse  boards,  classes,  216. 
panel,    arrangement    of    apparatus    for 

small,  243. 
panels,  238,  239. 
Testing  stations,  equipment,  397. 

location,  under  various  climatic  con- 
ditions, 396. 
trunk,  wire  chief's,  method  of  operating, 

182. 

Tests  to  ascertain  resistance  of  line,  380. 
circuit  for  preliminary,  181. 
for  locating  crosses,  procedure  in  making, 
386. 


INDEX 


417 


Tests,  faults  caused  by  broken  ends,  390. 
Theory  of  simplex  systems,  187. 
Timber,  selection  of,  for  poles,  260. 
Title  to  right-of-way,  246. 
Toll  board,  advantages  of  separate,  59. 
circuits,  auxiliary,  103,  145. 
combination  cord  circuit  for  multiple- 
drop,  82. 

equipments,  classification,  56. 
incoming  toll  trunk  for  non-multiple, 

72. 
recording  toll  trunk  for  non-multiple 

toll  board,  73. 

equipment  for  two-position,  64. 
Toll  connections  to  automatic  systems,  156. 
cut-in  station  for  grounded  lines,  34. 
key-type  equipment  at,  39. 
method  of  wiring  key  equipment  at, 

34- 

cut-in  stations,  29. 

drops  for  night  service,  method  of  trans- 
ferring, 61. 
equipments  illustrated,   use  of  various 

kinds,  57. 

line  construction,  245. 
terminal,  distribution  of  apparatus  in, 

explained,  148. 
method  of  cabling  in,  148. 
wiring,  148. 
lines,  line  wire  for,  247. 

for  night  service,  methods  of  trans- 
ferring, 60. 

and  local  lines  terminating  in  automatic 
switchboard,    complications   arising 
from,  156. 
Toll-to-local  connections  in  separate  toll 

and  local  three-wire  offices,  102. 
connections  in  three-wire  joint  toll  and 

local  offices,  96. 
in  two-wire  joint  and  local  offices, 

80. 
in  two-wire  separate  toll  and  local 

offices,  86. 

positions  at  local  switchboard,  42. 
switchboard,     Stromberg-Carlson     mul- 
tiple-drop, 97. 

switchboards,  different  types  of  equip- 
ments for,  56. 
multiple-drop,  75. 
multiple-lamp,  112. 
switching  systems,  55. 


Toll-to-toll  connection  in  magneto  multiple 

switchboard,  47. 
for  multiple-lamp  toll  boards,  gtti- 

eral  type,  112. 
with  repeating  coil,  43. 
at  small  magneto  switchboard,  42. 
transfer  circuit,  45. 
in  two-wire  joint  and  local  offices,  78. 
trunk,  busy-test  key  on  two-way,  74. 
Transfer  circuit  for  toll-to-toll  connection 

45- 

Transmission  by  inductance  loading,  Pu- 

pin's  method,  7. 

Van    Rysselberghe's    system    of    simul- 
taneous, 4. 

Transposing  lines  to  eliminate  disturbances, 

344- 
Transposition  poles,  location,  350. 

problem  complicated  by  paralleled  power 

and  telephone  lines,  365. 
schemes  for  ten  to  forty  wire  lines,  347. 
Transpositions,  method  of  cutting  in,  352. 

methods  of  making,  351. 
Tri-state  Telephone  and  Telegraph  Go's. 

equipment,  130. 

Trouble,  classes  of,  analyzed,  372. 
Troubles  due  to  placing  ringers  of  differ- 
ent resistances  on  same  line,  30. 
methods  of  testing  for  various,  370. 
Trunking  equipment,  arrangement,  69. 
Two-position  toll  boards,  equipment  for,  64. 
Two-way  toll  trunk,  busy-test  key  on,  74. 
Two- wire  system  equipment,  operation,  130. 


Underground  cables,  recent  developments 

in  loading,  232. 
United  States  Telephone  Co.,  equipment, 

138. 
Use  of  various  kinds  of  toll  equipments 

illustrated,  57. 


Van  Rysselberghe's  system  of  simultaneous 
transmission,  4. 

Various  types  of  guy  anchors,  289. 

Varley  loop  test,  383. 

Voltmeter  and  ammeter  circuits,  wiring, 

220. 

used  for  determining  nature  of  and  lo- 
cating troubles,  374. 


418  INDEX 

"Waterloo"  station  equipment,  32.  Wire,  stringing,  301. 

Wind  pressure  on  ice-coated  wire,  257.  apparatus  for,  302. 

on  poles,  269.                                  .  table  of  resistance  of  iron  and  copper, 

Wire  chief's  cord  circuit,  184.  376. 

desk  equipment,  174.        .  tensile  strength  o"f  different  sizes,  252, 

desk,  wiring  toll  line  circuit  at,  176.  253. 

testing  apparatus  to  toll  lines,  methods  Wires,   sag   of   telephone   and    telegraph, 

of  connecting,  described,  175.  259. 

circuit,  operation  of,  described,  178.  Wiring     for     straight     telephone     circuit, 

trunk,  method  of  operating,  182.  method,  228. 

Wire,  ice-coated,  wind  pressure  on,  257.  toll  line  circuit  at  wire  chief's  desk,  176. 

lines,  transposition  schemes  for  ten  to  toll  line  terminal,  148. 

forty,  347.  terminal  for  small  switchboard,  41. 

for  small  equipments,  directions  regard-  voltmeter  and  ammeter  circuits,  2     . 
ing  cabling  and  size,  241. 


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